1 Introduction to GIS1 Introduction to GIS 1.1 What Is a GIS? A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events

Geographical Information System (GIS)

HEET Consult Pvt. Ltd., Baluwatar, Kathmandu 1

1 Introduction to GIS

1.1 What Is a GIS? A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events that happen on earth. GIS technology integrates common database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps. These abilities distinguish GIS from other information systems and make it valuable to a wide range of public and private enterprises for explaining events, predicting outcomes, and planning strategies.

1.1.1 GIS Definition

Burrough (1986) defines GIS as “a set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes”

Aronoff (1989) gives a. general description of GIS as “any manual or computer-based set of procedures used to store and manipulate geographically-referenced data.”

More specifically, Aronoff (1989) defines GIS as a computer-based system that provides four sets of capabilities to handle georeferenced Dta: 1. Data input 2.Data management (Data Storage and Retrieval), 3. Manipulation and analysis, 4. Data Output

The major challenges we face in the world today--overpopulation, pollution, deforestation, natural disasters--have a critical geographic dimension.

Whether sitting a new business, finding the best soil for growing bananas, or figuring out the best route for an emergency vehicle, local problems also have a geographical component GIS will give you the power to create maps, integrate information, visualize scenarios, solve complicated problems, present powerful ideas, and develop effective solutions like never before. GIS is a tool used by individuals and organizations, schools, governments, and businesses seeking innovative ways to solve their problems.

Mapmaking and geographic analysis are not new, but a GIS performs these tasks better and faster than do the old manual methods. And, before GIS technology, only a few people had the skills necessary to use geographic information to help with decision making and problem solving.

Today, GIS is a multibillion-dollar industry employing hundreds of thousands of people worldwide. GIS is taught in schools, colleges, and universities throughout the world. Professionals in every field are increasingly aware of the advantages of thinking and working geographically.



1.2 Basic Concept of a GIS

GIS has had an enormous impact on virtually every field that manages and analyses spatially distributed data. For those who are unfamiliar with the technology, it is easy to see it as a magic box. The speed, consistency, and precision with which it operates is truly impressive. Moreover, its strongly graphic character is hard to resist. However, the experienced analyst sees the philosophy of GIS quite differently. With experience, GIS becomes simply an extension of one’s own analytical thinking. The system has no inherent answers, these depend upon the analyst. It is a tool, just like statistics is a tool. it is a tool for thought.

Investing in GIS requires more than an investment in hardware and software. Indeed, in many instances this is the least of concerns. Most would also recognize that a substantial investment needs to be made in the development of the database. However, one of the least recognized and most important investments is in the analysts who will use the system. The system and the analyst cannot be separated to put it simply; one is an extension of the other.

1.3 Evolution of GIS Revolution in information technology

• Computer Technology

• Remote Sensing

• Global Positioning System (GPS)

• Communication Technology

Rapidly declining cost of computer hardware

Enhanced Functionality of software

1.4 Why GIS? • 70% of the information includes some geographical Facts in the decision-making process

• Ability to assimilate divergent sources of data both spatial and non-spatial (attribute data)

• Visualization impact

• Sharing of information

• Analytical capability in a spatial context

Many professionals, such as foresters, urban planners, and geologists, have recognized the importance of spatial dimensions in organizing and analyzing information. Whether a discipline is concerned with the



very practical aspects of business, or whether a discipline is concerned with purely academic research, geographic information systems can introduce a perspective which can provide valuable insights.

1.5 History of GIS Canada was the pioneer in development of geographic information systems as a result of innovations dating back to the early 1960s. Much of the credit goes to Roger tomilson for the early development of GIS. Although the field of GIS has been around for the last 25 years, the real potentials hove become apparent only since the late 1980s.

Fig. GIS Historical Development

1.6 Spatial Operations Many computer programs can handle geographic data such as those described below.

1.6.1 Spreadsheets (e.g., lotus 1 -2-3, QuatroPro).

A spreadsheet can be thought of as a large imaginary piece of electronic paper that can contain information in rows and columns, which is used for all sorts of (mathematical) operations for producing graphs. Spreadsheets are often used in combination with GJS.

1.6.2 Database Management Systems (e.g., Oracle, dBase)

A Database Management System (DBMS) is a set of programs which is a collection of information about things and their relationships to each other and which maintain and manipulate data in a database. A DBMS only handles “attribute data” and cannot handle maps. It generally forms an integrated part of GIS.

1.6.3 Computer Aided Design (e.g., AutoCad)

CAD systems are for capturing and manipulating drawings. Point, line, and polygon objects are stored in vector format. A CAD system is like a part of a vector GIS. CAD software is highly developed and has very good display capabilities, but, on its own, it is neither designed to carry out spatial operations nor use raster data types.

Computer Science

CAD/CAM

Earth Science

Remote Sensing

Military Studies

Cartography

Spatial Mathmatics

Urban Planning

Surveying and Civil Engineering

Geography

GIS



1.6.4 Cartographic packages (e.g. Aldus Freehand, CarthoGraphix)

Cartographic packages or desktop mopping systems are for selective search and display of information from spatial databases and For the production of high quality output maps which meet cartographic standards. In this sense, they form a useful addition to GIS, since the output Facilities of most GIS are still unsatisfactory.

1.6.5 Photogrammetrical software (e.g. DMS)

Photogrammetrical packages are designed to take point sample data (mostly of terrain elevations) from aerial photographs, satellite images, and GPS (global positioning systems) data, and then produce digital elevation models (DEM) and contour maps. They form an important input source for GIS.

1.6.6 Image Processing Software (e.g., ERDAS)

Image processing software is designed to handle satellite images, or scanned aerial photographs. The information from such images can be extracted by several kinds of image enhancement techniques and classification methods. Output maps from image processing software often form the input into GIS. These software packages are not considered to be GIS. The difference between GIS and other software using geographic data is that only GIS permit spatial operations on the data.

1.7 Spatial Objects

Spatial Objects or Spatial Individuals for Geographic Features are the things located on or near the surface of the earth. Geographic features can occur naturally. (forest, river) can be found with man made constructions (road, power pole) and can be subdivisions of land (political divisions).

1.7.1 Geometry and attributes of Spatial objects

Points, Its ID and Attributes

Lines, Its IDs and Attributes

Polygons, Its IDs and Attibutes

Gis and Other sources

C B

B A

C A B









1.8 What Can GIS Do for You?

1.8.1 Perform Geographic Queries and Analysis

The ability of GISs to search databases and perform geographic queries has saved many companies literally millions of dollars. GISs have helped reduce costs by

• Streamlining customer service.

• Reducing land acquisition costs through better analysis.

• Reducing fleet maintenance costs through better logistics.

• Analyzing data quickly, as in this example:

A realtor could use a GIS to find all houses within a certain area that have tiled roofs and five bedrooms, then list their characteristics.

The query could be further refined by adding criteria - the house must cost less than $100 per square foot. You could also list houses within a certain distance of a school.

1.8.2 Improve Organizational Integration

Many organizations that have implemented a GIS have found that one of its main benefits is improved management of their own organization and resources. Because GISs have the ability to link data sets together by geography, they facilitate interdepartmental information sharing and communication. By creating a shared database, one department can benefit from the work of another - data can be collected once and used many times.



As communication increases among individuals and departments, redundancy is reduced, productivity is enhanced, and overall organizational efficiency is improved. Thus, in a utility company the customer and infrastructure databases can be integrated so that when there is planned maintenance, affected customers can be sent a computer-generated letter.

1.8.3 Make Better Decisions

The old adage "better information leads to better decisions" is as true for GIS as it is for other information systems. A GIS, however, is not an automated decision making system but a tool to query, analyze, and map data in support of the decision making process. GIS technology has been used to assist in tasks such as presenting information at planning inquiries, helping resolve territorial disputes, and siting pylons in such a way as to minimize visual intrusion.

GIS can be used to help reach a decision about the location of a new housing development that has minimal environmental impact, is located in a low-risk area, and is close to a population center. The information can be presented succinctly and clearly in the form of a map and accompanying report, allowing decision makers to focus on the real issues rather than trying to understand the data. Because GIS products can be produced quickly, multiple scenarios can be evaluated efficiently and effectively.

1.8.4 Making Maps

Maps have a special place in GIS. The process of making maps with GIS is much more flexible than are traditional manual or automated cartography approaches. It begins with database creation. Existing paper maps can be digitized and computer-compatible information can be translated into the GIS. The GIS-based cartographic database can be both continuous and scale free. Map products can then be created centered on any location, at any scale, and showing selected information symbolized effectively to highlight specific characteristics.

The characteristics of atlases and map series can be encoded in computer programs and compared with the database at final production time. Digital products for use in other GISs can also be derived by simply copying data from the database. In a large organization, topographic databases can be used as reference frameworks by other departments.

1.9 Component of GIS

A working GIS integrates five key components: hardware, software, data, people, and methods.

1.9.1 Hardware

Hardware is the computer on which a GIS operates. Today, GIS software runs on a wide range of hardware types, from centralized computer servers to desktop computers used in stand-alone or networked configurations.



1.9.2 Software

GIS software provides the functions and tools needed to store, analyze, and display geographic information. Key software components are

• Tools for the input and manipulation of geographic information

• A database management system (DBMS)

• Tools that support geographic query, analysis, and visualization

• A graphical user interface (GUI) for easy access to tools

1.9.3 Database

Possibly the most important component of a GIS is the data. Geographic database and related tabular data can be collected in-house or purchased from a commercial data provider. A GIS will integrate spatial data with other data resources and can even use a DBMS, used by most organizations to organize and maintain their data, to manage spatial data.

1.9.4 People (Users)

GIS technology is of limited value without the people who manage the system and develop plans for applying it to real-world problems. GIS users ranged from technical specialists who design and maintain the system to those who use it to help them perform their everyday work.

1.9.5 Methods (Policy and Procedures)

A successful GIS operates according to a well-designed plan and business rules, which are the models and operating practices unique to each organization.

1.10 How GIS Works ? A GIS stores information about the world as a collection of thematic layers (like: rivers, roads, forests, land use, geology, etc) that can be linked together by geography. This simple but extremely powerful and versatile concept has proven invaluable for solving many real-world problems from tracking delivery vehicles, to recording details of planning applications, to modeling global atmospheric circulation.

1.10.1 Geographic References

Geographic information contains either an explicit geographic reference, such as a latitude and longitude or national grid coordinate, or an implicit reference such as an address, postal code, census tract name, forest stand identifier, or road name. An automated process called geocoding is used to create explicit geographic references (multiple locations) from implicit references (descriptions such as addresses). These geographic references allow you to locate features, such as a business or forest stand, and events, such as an earthquake, on the earth's surface for analysis.

1.10.2 Vector and Raster Models

Geographic information systems work with two fundamentally different types of geographic models--the "vector" model and the "raster" model. In the vector model, information about points, lines, and polygons is encoded and stored as a collection of x,y coordinates. The location of a point feature, such as a bore hole, can be described by a single x,y coordinate. Linear features, such as roads and rivers, can be



stored as a collection of point coordinates. Polygonal features, such as sales territories and river catchments, can be stored as a closed loop of coordinates.

The vector model is extremely useful for describing discrete features, but less useful for describing continuously varying features such as soil type or accessibility costs for hospitals. The raster model has evolved to model such continuous features. A raster image comprises a collection of grid cells rather like a scanned map or picture. Both the vector and raster models for storing geographic data have unique advantages and disadvantages. Modern GISs are able to handle both models.

1.11 GIS Tasks

General purpose geographic information systems essentially perform six processes or tasks:

• Input

• Manipulation

• Management

• Query and Analysis

• Visualization

1.11.1 Input

Before geographic data can be used in a GIS, the data must be converted into a suitable digital format. The process of converting data from paper maps into computer files is called digitizing.

Modern GIS technology can automate this process fully for large projects using scanning technology; smaller jobs may require some manual digitizing (using a digitizing table). Today many types of geographic data already exist in GIS-compatible formats. These data can be obtained from data suppliers and loaded directly into a GIS.

1.11.2 Manipulation

It is likely that data types required for a particular GIS project will need to be transformed or manipulated in some way to make them compatible with your system. For example, geographic information is available at different scales (detailed street centerline files; less detailed census boundaries; and postal codes at a regional level). Before this information can be integrated, it must be transformed to the same



scale (degree of detail or accuracy). This could be a temporary transformation for display purposes or a permanent one required for analysis. GIS technology offers many tools for manipulating spatial data and for weeding out unnecessary data.

1.11.3 Management

For small GIS projects it may be sufficient to store geographic information as simple files. However, when data volumes become large and the number of data users becomes more than a few, it is often best to use a database management system (DBMS) to help store, organize, and manage data.A DBMS is nothing more than computer software for managing a database.

There are many different designs of DBMSs, but in GIS the relational design has been the most useful. In the relational design, data are stored conceptually as a collection of tables. Common fields in different tables are used to link them together. This surprisingly simple design has been so widely used primarily because of its flexibility and very wide deployment in applications both within and without GIS.

1.11.4 Query and Analysis

Once you have a functioning GIS containing your geographic information, you can begin to ask simple questions such as

• Who owns the land parcel on the corner?

• How far is it between two places?

• Where is land zoned for industrial use?

And analytical questions such as

• Where are all the sites suitable for building new houses?

• What is the dominant soil type for oak forest?

• If I build a new highway here, how will traffic be affected?

GIS provides both simple point-and-click query capabilities and sophisticated analysis tools to provide timely information to managers and analysts alike. GIS technology really comes into its own when used to analyze geographic data to look for patterns and trends and to undertake "what if" scenarios. Modern GISs have many powerful analytical tools, but two are especially important.

1.11.4.1 Proximity Analysis

• How many houses lie within 100 m of this water main?

• What is the total number of customers within 10 km of this store?

• What proportion of the alfalfa crop is within 500 m of the well?

To answer such questions, GIS technology uses a process called buffering to determine the proximity relationship between features.



1.11.4.2 Overlay Analysis

The integration of different data layers involves a process called overlay. At its simplest, this could be a visual operation, but analytical operations require one or more data layers to be joined physically. This overlay, or spatial join, can integrate data on soils, slope, and vegetation, or land ownership with tax assessment.

1.11.5 Visualization

For many types of geographic operation the end result is best visualized as a map or graph. Maps are very efficient at storing and communicating geographic information. While cartographers have created maps for millennia, GIS provides new and exciting tools to extend the art and science of cartography. Map displays can be integrated with reports, three-dimensional views, photographic images, and other output such as multimedia.

1.12 Data for GIS

What Map Data Do I Need?

If you are unfamiliar with map data, think first about how you want to use map data. Many project needs are met with the following common map data types. Then explore these links to learn more about map data!

Base Maps--Include streets and highways; boundaries for census, postal, and political areas; rivers and

lakes; parks and landmarks; place names; and USGS raster maps.



Business Maps and Data--Include data related to census/demography, consumer products, financial services, health care, real estate, telecommunications, emergency preparedness, crime, advertising, business establishments, and transportation.

Environmental Maps and Data--Include data related to the environment, weather, environmental risk, satellite imagery, topography, and natural resources.

General Reference Maps--World and country maps and data that can be a foundation for your database.

1.13 How Do I Get Map Data? Fortunately, volumes of existing geographic data are readily available. Through the ArcData Publishing Program, ESRI has established a partnership with leading commercial data vendors to provide a wealth of information in a plug-n-play format for use with ArcView GIS. ESRI's GIS Store and ArcData Online both offer a convenient way to get the most popular geographic data.

And, a variety of useful geographic data come bundled with ArcView GIS to help you get started quickly.

These data sets can be used as the foundation for your GIS projects or to supplement your existing data.

1.13.1 Methods In Nepal

• Existing maps

• Field Survey

• Digital data available in Departments of Survey, Min Bhawan, Kathmandu, Nepal

• ICIMOD

1.14 TOPOGRAPHICAL MAP INTERPRETATION

1.14.1 Definition of Map

The presentation of three dimensional geographic objects/features in two dimensional plane can be described a map. In general, maps are drawn to a reduced form. However, if the object or feature is very small, such matters are presented in an enlarge form. For example, the map of an area is very small compared to the real feature, but a map of a small object, viz. seed of mustard, Sissau tree is generally greater than their physical size.



The real object or a feature can be projected to a two dimensional plane by using two type of projections:

− Perspective Projection − Orthographic Projection

A. Perspective Projection

While preparing a perspective projection, the observer stands at a point and sights the object. The imaginary lines of sight joining the observation point, object and the plane under consideration gives the projection of the object. The projections obtained by torch light, cinema, aerial photographs can be considered as an examples of perspective projection. While projecting the object this way, the object can lose its shape and size. The middle part of the object remains unchanged, however, the shape and size of the features away from the center may differ.

B. Orthographic Projection

The projection of an object or feature to the plane parallel to the plane, where the object is lying is an orthographic projection. Straight and vertical lines from different points of the object are drawn between these planes, thereby projecting the real shape and size of the object.

1.1 Object to be

Plane of projection

123

1 2 3



1.14.2 Latitudes and Longitudes The imaginary lines joining North and South poles and passing through the surface of the earth are known as Latitudes. They are nearly semi-circle in shape. Whereas , the maginary lines drawn along east-west direction are called latitudes. The longest line passing through the center of the earth is known as Equator.

Plane of Projection

1.1.1 Object to be projected



1.14.3 Map Scale The ratio of dimension of an object in reality to that in the map is known as scale. If an object having a length of 250 m (25,000 cm) for example is represented by one cm on a map, the scale is 1:25000. Usually, topographical maps are prepared in scales of 1:1000,000, 1:500,000, 1:125,000, 1:100,000, 1:50,000, 1:25,000, and 1:10,000. The bigger the scale, the smaller the map. Scale can also be represented by a bar as given below. The advantage of a bar scale over a numeric scale is that the information is not changed when the map is enlarged or reduced the bar scale presented on a map is also resized accordingly.

1.14.4 Symbols The signs or signals used in a map to provide various pieces information are known as symbols. The usual symbols used in a topographical map are of buildings, schools, post office, village, trail, road, rivers, forest, landslide area etc.

1.14.5 Contours The value of a plan or map is highly enhanced if the relative position of the points is represented both horizontally as well as vertically. Such maps are known as topographic maps. Thus, in a topographic survey, both horizontal as well as vertical controls are required. The position of an object in vertical plane in a map is represented by contour. These are imaginary lines joining the points of equal elevations.

1.14.6 Characteristics of Contours The following characteristic features may be used while plotting or reading a contour plan: 1. Except for an overhanging cliff or a cave, two contour lines of different elevations cannot

cross each other except in the case . of 2. Contour lines of different elevations can unite to form one line, only in the case of a

vertical cliff.

0 m 100 200 300

North Pole

Latitude

Equator

Latitude

South Pole



3. Contour lines close together indicate steep slope. They indicate a gentle slope if they are far apart. If they are equally spaced, uniform slope is indicated. A series of straight, parallel and equally spaced contours represents a plane surface.

4. A contour passing through any point is perpendicular to the line of steepest slope at that point. This agrees with (3), since the perpendicular distance between contour lines is the shortest distance.

5. A closed contour line with one or more higher ones inside it represents a hill; similarly, a closed contour line with one or more lower ones inside it indicates a depression without an outlet .

6. Two contour lines having the same elevation cannot unite and continue as one line. Similarly, a single contour cannot split into two lines.

7. A contour line must close upon itself, though not necessarily within the limits of the map. 8. Contour lines cross a watershed or ridge line at right angles. They form curves of U-

shape round it with the concave side of the curve towards the higher ground 9. Contour lines cross a valley line at right angles. They form sharp curves of V-shape

across it with convex side of the curve toward the higher ground.

1.14.7 Forms of contour

Contour have different forms. Some of them are as follows: Evenly distributed contours (contour spacing is constant), denotes a planer slope Concave contours (Valley or gully) Convex contours (Spur or ridge) Saddle Closed contours (for represeting a hill or depression

200

400 600

400 200

600

400 600

200

600 400

600 700

Saddle 300 400 500 500 400 300 200

300 400 500 500 400 300 200



Dense contours, rare contours, and very rare contours

Cliffs and overhangs

1.14.8 Drainage pattern The shape of streams, rivers shown in a topographical map are known as drainage pattern. Some of them are presented below: Dendritic Drainage pattern Parallel Drainage Pattern Trellis Drainage Pattern Rectangular Drainage Pattern Centripetal Drainage Pattern Radial Drainage Pattern

Steep slope Gentle slope Very gentle slope

Cliff

400 300 200

400 300 200 100 100

Overhang



1.14.9 Stream Order The rivers shown in a topographicl map can be categorised into different types as shown in fig.

1.14.10 Conclusion The information given and shown in the topographical maps enables technical personnel to er know about the particular location or site in detail, therefore, they have to have ample knowledge of such maps.

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USERS

GIS

SOFTWARETOOLS DATABASE

ABSTRACTIONOR

SIMPLIFICATION

RESULTS

Components of GIS

+

THE REAL WORLD

2 Components of GIS

Several components are involved in GIS technology.

2.1 Hardware A computer and the associated peripherals are essential for handling spatial data in GIS. These devices are collectively known as hardware.

2.2 Software Software refers to the programmes that run on computers; these include programmes to manage the computer and to perform specific functions. For example, Lotus, dBase, WordPerfect, and ARC/INFO are specialised software programmes designed to perform certain tasks.

2.3 Database A central theme to GIS is the database. A GIS database deals with spatial data. GIS facilitate integration of spatial and attribute data and this makes GIS unique in contrast to other database systems. The beauty of GIS technology lies in the ability to assimilate disparate sources of data and analyse them.

2.4 Human Input People who work with GIS form the most important component. GIS constitute truly a interdisciplinary field and require varied backgrounds of expertise, depending upon the applications. In addition, for technical management, a Hardware Specialist, System Administrator, and Database Manager are required for a corporate GIS set-up.

2.5 Policy and Procedures A methodology is a must to derive the results users need. Basically, this includes spatial analysis for the particular application. By and large, this depends upon the institutional framework and its interest in exploiting GIS technology for decision-making



H hard-ware

computer, periphery (digitizer, scanner, plotter)

~ 4 years

S soft-ware

programs, methods ~ 7 years

D data data, rules, knowledge ~ 25 years

U user

H hard-ware

computer, periphery (digitizer, scanner, plotter)

~ 4 years

S soft-ware

programs, methods ~ 7 years

D data data, rules, knowledge ~ 25 years

U user

HH hard-warehard-ware

computer, periphery (digitizer, scanner, plotter)computer, periphery (digitizer, scanner, plotter)

~ 4 years~ 4 years

SS soft-waresoft-ware

programs, methodsprograms, methods ~ 7 years~ 7 years

DD datadata data, rules, knowledgedata, rules, knowledge ~ 25 years~ 25 years

UU useruser

2.6 Life time of the components The cost Pyramide

Data 80%

Software, maintenance, training 15%

Hardware 5%


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2.7 GIS Products


3 SPATIAL DATA AND THEIR REPRESENTATION

3.1 Introduction The collection of data about the spatial distribution of significant properties of the earth's surface has long been an important part of the activities of organized societies. From the earliest civilizations to modern times spatial data have been collected by navigators, geographers, and surveyors and rendered into pictorial forms by the mapmakers or cartographers. Those were the maps basically used by the sailors and military purposes. But for last few hundred years maps are becoming common for many activities. Therefore, the spatial data refers data closely associated with the space.

3.2 Definition of Map The history says us the early human beings used to transfer their feelings to other persons and community through articulacy (by speaking), literacy (by writing), numeracy (by counting) and graphicacy (by picture). These were the four major inventions started with the pace of human civilization. The language of graphics was an important media for transferring their feelings and information to other persons and community before the development of other language. The present-day map is the product of the skill of graphicacy. The map may be defined as the representation of the earth’s pattern as a whole or a part of it. In other word we can say that the map is the reduced form of the earth’s surface or parts of it to make visualized and presented in a piece of paper or something else. The human mind seems highly receptive to the graphics compared to the other media of transforming the feelings and information. It is said that ‘a map worth thousands of words’. That means a map helps us to summarize the things through a receptive manner of audience or reader. A map consists conventional signs, drawn to a scale and with certain projection system so that each and every point on it corresponds to the actual terrestrial or celestial position. Maps are usually drawn to show different details on a large or small scale. Similarly, the content or information of a map is equally important. Because of this, the types of maps are categorized based on these two basic parameters.

3.3 Types of Map The types of Map can be grouped by its

(i) scale of representation and (ii) the information/contents which it has carries.

Based on the scale we can categories the map in – large scale, medium scale and small scale. There is not any strict limit for the delineation but, in general, the large-scale map can be depicted for the maps with larger than 1:100,000. Some times these maps can be 1:5000 or larger. The Cadastral map of Nepal is 1:625, 1:1250 and 1:2500. The medium scale map is larger than 1:100,000 to 1:500,000 scale. Similarly, the small-scale map becomes larger than 1:500,000 scales or more.


Types of Geographical phenomena

Geographic information is commonly broken into the components of space, time, and attribute.


Space – Refers to the objects or phenomena confined in the outer crust of the surface. Those data

could be referred in two ways, i.e. in terms of relative reference of the object, and the standard

system of coordinates. All the objects followed the positional standpoint on the surface and most of

the database handled in the GIS system handle the standard system of coordinates under the two

dimensional ‘Cartesian’ space. In the real world, the geographical or spatial data are occurring in

four identifiable types: points, lines, areas and surfaces. From the basic topological concepts, the

data can be reduced to – the point, the line, and the area.

Time - The spatial data have often a role of ‘temporal reference’. Of course, time is not visible in

the map or space, however, it signifies the importance of the spatial data. The space-time relationship

constructs a relative space that differs from the abstract dimensions.


Attribute - The geographic data can range from observable physical properties to aesthetic judgments, values and characteristics. Those are the attribute information. An attribute value is a specific instance of the characteristic associated with a geographic feature. For example; house and household number, building material, number of storey, area occupied etc.


We may have different maps with different purposes. Similarly we can produce different types of spatial information to obtain different objectives.




Geographic Objects

For the Geographic objects we can take an example of geographic data related with the District Planning Location of the district Administrative division of the district (VDC, Ilaka and Constituency Division of the district) Altitude Slope Relief Geological structure Soils type River systems/density Aspect Annual mean rainfall zone Land use/cover-1999 Settlement with population Ethnicity of population Population by religion House by roof types Occupational structure Crude density of the population Distribution of road facility Education facility Health facility Drinking water facility Irrigation facility Electricity facility Postal services Banking services Tele communication services Cooperative services Agriculture input services Veterinary services Distribution of motor road accessibility to the settlement Distribution of accessibility to primary school Distribution of accessibility to lower secondary school Distribution of accessibility to secondary school Accessibility to health services Accessibility of postal services Development Status of the VDC Illiteracy level Unnatural death level Unsafe water users level Health service level Malnutrition level Food deficiency level


Women’s landholding Female illiteracy level Human poverty level Tourism Center Etc…… Computer Representation of Geographic Information

i. The map is a graphic or analog representation of geographic phenomena. The computer handled the spatial information in Digital from.

Geographic data can be grouped in accordance with their entities i.e. vector and raster. The vector geographic data have their topology but the raster have their cell value. In computer both data structure have different system of representation. The vector data representation based on the Cartesian System of coordinate and the topology records in the Feature Attribute Table (FAT). Each topology types have distinct type of FAT and those records on their dBASE file. While the raster data structure have their cell value and the information records on Row and Column form.

GEOGRAPHIC DATABASEGEOGRAPHIC DATABASEGEOGRAPHIC DATABASE

MAPMAP

ANALYSISNew data

relationships

ANALYSISNew data

relationships

Kathmandu

Valley

GIS

REPORT


Zoning

1

3

2

4 ZONING.PAT

0 -1 IND2 RES3 COM4 RES

ZONING-ID ZONE

ROADBUF.ID INSIDEROADBUF.PAT

0 10 100

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0 - 11 IND 12 RES 1003 COM 1004 RES 1. . .. . .

634

RDZONE(features are combined)

2

13 1211

51 8

9

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11 3

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0 10 100

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TOPOLOGICOVERLAY

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RDZONE.PATRDZONE.PAT

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634 634 634 634


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Road.buf

7

Road.buf

7

M a p 2

M a p 1

C o m p o s i t e M a p

AB

CX

ZA , X

B , Y

C , YB , Z

Y B , X

C , Z

A , Z

M a p 2

M a p 1

M a p 2

M a p 1M a p 1

C o m p o s i t e M a p

AB

CX

ZA , X

B , Y

C , YB , Z

Y B , X

C , Z

A , Z

AB

CX

ZA , X

B , Y

C , YB , Z

Y B , X

C , Z

A , Z


4 Spatial Data Acquisition

4.1 INTRODUCTION

Since 1998 there has been a massive increase in the use of GIS, intensified by the lower cost of hardware required to run advanced GIS packages. Standard desktop PCs now have the power to run GIS software, and the GI market has, as a consequence, opened up dramatically. However, any GIS is only as good as the data it handles. With the environment constantly changing, and with new market sectors enjoying the benefits of GIS, the collection of new data and the maintenance of existing data has become the most time consuming and costly aspect of GIS implementation. As a consequence, users are in a constant quest for the most effective way of collecting and managing GIS data.

4.2 DATA SOURCE

Geographic data are generally available in two forms

Analog data – a physical product displaying information visually on paper or film

Digital data – information formatter or a computer readable file

4.2.1 Analog :

A number of different sources are available • Standardized map sheets

• Digital data

Figure 1: Sources of Geographic Data

• Analogue data


• Mylar map transparencies • Aerial photos • Tabular Data • Written reports

4.2.2 Digital :

There are number of different type's data sets which can be purchased and directly used in a GIS. Some of them are listed below

• DEM – Digital Elevation Model, files from the US Geological Survey (Elevation Data) • Digital satellite data can be obtained at different resolutions from various sources • Other data can be obtained in digital format such as DXF or SIF data files, which are generated by other software

There are two types of data sources:

1. Primary data: Data measured directly by surveys, field data collection, remote sensing 2. Secondary data: Data obtained from existing maps, tables or other data sources There are five types of different data capturing systems (Figure 3) commonly used in a GIS: • Manual Digitization • Key Punching • Global Positioning System • Remote Sensing • Scanning

Satellite

Remote Sensing Scanning

Digitizing

GPSAerialPhotography


4.3 COORDINATE SYSTEM

The Geographic Coordinate system is a spherical coordinate system composed of parallels of latitude and meridians of longitude. Both divide the circumference of the earth into 360 degrees which are further subdivided into minutes and seconds. Unlike the equator in the latitude system, there is no natural zero meridian. In 1884, it was finally agreed that the meridian of the Royal Observatory in Greenwich, U.K., would be the Prime Meridian.

Advantages of geographic coordinates: one system for the entire earth more or less conform to the shape of the earth, so no systematic distortions easy to map in different map projections

Disadvantages of geographic coordinates:

spherical, not plan metric coordinates must use spherical trigonometry to measure areas and distances must project onto flat maps where the grid lines are curved

A) The Shape of the Earth The shape of the Earth can be represented by an ellipsoid of rotation (or called a spheroid) with the

lengths of the major semi-axis (a) and the minor semi-axis (b) as shown in Figure 2.11 (a)

Spherical coordinate system Cartesian coordinate system

Figure 4: Coordinates System

(0, 0)

Data usually here

y-axis

origin

(a) Ellipsoid (b) Geodetic Coordinates (c) Geometric Coordinates

Figure 5: Earth’s Shape


The amount of polar flattening (or called ellipticity) is expressed by

The approximate values of the Earth are : a=6,378 km , b=6,356 km, a-b= 22km, f=1/298 However, the major and minor semi-axes have been measured precisely by many scientists or organizations that have adopted in different countries. a) local ellipsoid: It defines the origin and orientation of latitude and longitude lines. A local datum aligns its spheroid to closely fit the Earth’s surface in a particular area and its 'origin point' is located on the surface of the Earth. The coordinates of the 'origin point' are fixed and all other points are calculated from this control point. The coordinate system origin of a local datum is not at the center of the Earth. NAD27 and the European Datum of 1950 are local datums. Figure 6: Local Ellipsoid Figure 7: Global best-fitted ellipsoid Calculation of a map projection requires definition of the spheroid. As the earth is not a perfect globe (i.e., the earth is 'flattened' at the poles), a spheroid is defined in terms of axis lengths and eccentricity of the earth. Several principal spheroids are in use by one or more countries. Differences are due primarily to calculation of the spheroid for a particular region of the earth's surface. Some important spheroids are the Clarke 1866, the Bessel and the New International 1967. In the HKH Region, in general the Everest spheroid is applied.

abaf −

=


Year

Name of Ellipsoid

Length of semi-axes(m) Major (a) Minor (b)

Ellipticity (t)

Areas of use

1984 WGS-84 6378 137 6356 752 298.2572 GPS 1980 GRS-80 6378 136 6356 752 298.257 IUGG 1940 Krasovsky 6378 245 6356 863 298.3 Russia 1924 International 6378 388 6356 912 297 Europe, China,

South America 1880 Clarke 1880 6378 249 6356 515 293.46 Africa,

Middle East 1866 Clarke 1860 6878 206 6356 584 294.89 USA, Canada,

Philippines 1841 Bessel 6877 397 6356 079 299.15 Japan, Korea,

Indonesia 1830 Everest 6377 304 6356 103 300.80 India, Myanmar

Malaysia b) global best-fitted ellipsoid: In the last fifteen years, satellite data has provided geodesists with new measurements to define the best Earth-fitting ellipsoid, which relates coordinates to the Earth’s center of mass. An Earth-centered, or geocentric, datum does not have an initial point of origin like a local datum. The Earth’s center of mass is, in a sense, the origin. The most recently developed and widely used datum is the World Geodetic System of 1984 (WGS84). It serves as the framework for supporting locational measurement worldwide. GPS measurements are based upon the WGS84 datum. Ellipsoids or Spheroids Semi-Major Axis of Ellipsoid Semi-Minor Axis of Ellipsoid Standard Parallel The standard parallel refers to the one or two lines of latitude along which the cone is tangent to the earth. Maps in the Conic projections normally give the coordinates for the standard parallels. Central Meridian The single line of longitude that is truly vertical on the map. It is usually in the middle of the map. Map in the Conic projection normally give the coordinates for the central meridian. False Easting Many projections have an original point which might be located at the intersection of the CM and SP or the CM and the latitude of the projection’s origin.


The False Easting is the X-coordinate value assigned relative to this origin. For instance, if the origin of projection (in latitude/longitude) is in the center of the map, all areas west of the origin would be negative when False Easting of zero is assigned. To make the coordinate positive for the entire map, set the False Easting to a positive number. False Northing The false northing is similar to false Easting except that it is an arbitrary Y-shift. For instance, if the origin of projection (in latitude/longitude) is in the center of the map, all areas south of the origin would be negative unless a positive False Northing was assigned. Latitude of Projection’s Origin For conic projection where two standard parallels are assigned. The latitude of the projection’s origin identifies where to put the false Easting and Northing. XSHIFT or YSHIFT The constant to add to the input coordinate. Datum Selecting a specific reference ellipsoid to use for a specific area, and orientation it to the landscape, defines what is known in geodesy as a datum. Parameters of the datum 1. The origin of the three axes is fixed to the earth’s center of mass 2. The Z axis passes through the north and south poles, i.e..... the rotation axis 3. The X axis passes through the intersection of the equator and the Greenwich Meridian 4. The Y axis is orthogonal to other two axes 5. Scale Transformation of Datum It is considered when using GPS data.Seven parameter transformation 1. X, Y, Z Shift of the origin ( 3 parameters) 2. Rotation about each axis ( 3 parameters) 3. Scale factor ( 1 parameter) Three Parameter Transformation Molodensky Transformation Most of the older datum have parallel Z axis. Also the scale factors are usually very close to 1. For this reason, rotation and scale factor are sometimes ignored and only the three translation are used. Molodensky developed the formulae to allow the three parameter shift and the change in ellipsoidal parameters to be performed in one operation. This technique is widely used for mapping purposes, if meter level GPS data is being transformed to small scale mapping then it may be well adequate. However, it is likely to only be accurate to a few meters and, as such, is not an appropriate strategy on it’s own for transformation of high accuracy. In the same way as the seven parameter transformation, a precise base WGS84 station coordinate is necessary, rather than using published three parameter transformation alone.


4.4 MAP PROJECTION A map projection is a process of transforming location on the curved surface of the Earth with the geodetic coordinate (ϕ,λ) to planer map coordinates (x,y). More than 400 different map projections have been proposed. The map projections are classified by the following parameters projection plane : perspective ,conical , cylindrical aspect : normal , transverse , oblique property: conformality, equivalence , equidistance Mercator is an international rectangular coordinate system which extends around the world from 84 degrees North to 80 degrees South. The world is divided into 60 zones, each covering six (6) degrees longitude. Each zone extends three (3) degrees eastwards and three degrees westwards from its central meridian. Zones are numbered west to east from the 180 degree meridian. Because of the small area covered by each zone, a high degree of accuracy is possible. For example, Nepal falls under zones 44 and 45.

2 C li d i l P j ti

Conic Projection

Figure 8: Map Projections


Figure 9 : Universal Transverse Mercator (UTM) System Problems arise when a map extends into two UTM zones. The entire map will then have to be projected into one of the two zones. The advantage of using UTM coordinates is its metric nature. Normal calculations can be performed on UTM coordinates, while for geographic coordinates the minutes and seconds have to be first transformed into the decimal system. 4.5 GEO-REFERENCING All spatial data files need to be geo-referenced. Geo-referencing refers to the location of a layer or coverage in space as defined by co-ordinate referencing system. The geo-relational approach involves abstracting geographic information into a series of independently layers or coverage’s each representing a selected set of closely associated geographic features (e.g. roads, landuse, river, settlements, etc.). Each layer is a theme of geographic feature and the database is organized in the thematic layers.


Figure 10 : Georeferencing With this approach users can combine simple feature sets representing complex relationship in the real world. This approach borrows heavily the concepts of relational DBMS, and it is typically closely integrated with such systems. This is fundamental to database organization in GIS. DATA INPUT For attribute data:

Spreadsheets Database management systems

For geographic data: Coordinate entry Digitizing Scanning

Conversion of hardcopy to digital maps is the most time-consuming task in GIS –Up to 80% of project costs –Estimated to be a US $10 billion annual market –Labor intensive, tedious and error-prone –Database development sometimes becomes an end in itself Keyboard entry Keyboard entry of coordinate data, e.g., point latitude/longitude coordinates

–From a gazetteer (a listing of place names and their coordinates) –From locations recorded on a map

Coordinate conversion

MYLAR

ACETATE

Fig 11 : Manual Digitization

real world map

rotation 2 translations, scale

object

control point


Generally, latitude is y-coordinate, longitude is x-coordinate. Often they need to convert from degrees, minutes, seconds (DMS) to degrees decimal (DD) DD = D + M * (1/60) + S * (1/3600) Digitizing Manual digitizing still is the most common method for entering maps into a GIS. The map to be digitized is affixed to a digitizing table, and a pointing device (called the digitizing cursor or mouse) is used to trace the features of the map. These features can be boundary lines between mapping units, other linear features (rivers, roads etc.) or point features (sampling points, rainfall stations etc.). The digitizing table electronically encodes the position of the cursor with a precision of a fraction of a millimeter. The most common digitizing table uses a fine grid of wires, embedded in the table. The vertical wires will record the y coordinates, of the horizontal ones, then x coordinates. The range of digitized coordinates depends upon the density of the wires (called digitizing resolution) and the settings of the digitizing software. A digitizing table is normally a rectangular area in the middle, separated from the outer boundary of the table by a small rim. Outside of this so-called active area of the digitizing table, no coordinates are recorded. The lower left corner of the active area will have the co-ordinates x=0 and y=0. Therefore, make sure that the (part of the) map that you want to digitize is always fixed within the active area. On screen versus tablet

on-screen digitizing (heads-up digitizing) • tablet (heads-down digitizing) • raster map as background, vector layer in the foreground • better overview • scanning of maps necessary • no scanning necessary • special snap-functions • internal resolution • zooming => no internal resolution of digitizing • no snap functions • slow • fast

Digitization process 1. Fix map or aerial photograph on digitizing table 2. Select control points (tics): easily identifiable points with known real-world coordinates (e.g.,

road intersections, graticule intersections, mountain peaks) 3. Trace features to be digitized with pointing device (cursor)

Point mode: click at positions where direction changes Stream mode: digitizer automatically records position at regular intervals or when cursor moved a fixed distance

Digitizing errors Any digitized map requires considerable post-processing • Check for missing features • Connect lines • Remove spurious polygons • Some of these steps can be automated


Figure 12 : Digitizing errors and correction SCANNING Electronic detector moves across map and records light intensity for regularly shaped pixels •Scanner output is a raster data set •Usually needs to be converted into a vector representation –Manually (on-screen digitizing) –Automated (raster-vector conversion) line-tracing - e.g., MapScan •Often requires considerable editing •Automated vectorization: operator sets “global parameters” and system converts entire map •Interactive line following: operator points at specific line and system follows and converts the line

Undershoots

Dangles

Spurious polygons


Figure 13: An electronic scanning device will convert some types of Map information to digital form.

HEET Consult Pvt. Ltd., Baluwatar, Kathmandu

46

5 Introduction to Remote Sensing Remote Sensing is the transport of information from an object to a receiver (observer) by means of radiation transmitted through the atmosphere. The interaction between the radiation and the object of interest conveys information required on the nature of the object (eg. reflection coefficient, emittance, roughness). Passive Remote Sensing makes use of sensors that detect the reflected or emitted electro-magnetic radiation from natural sources. Active Remote Sensing makes use of sensors that detect reflected responses from objects that are irradiated from artificially-generated energy sources, such as radar. The Electro-Magnetic Radiation (EMR), which is reflected or emitted from an object, is the usual medium to carry information in remote- sensing. However, any medium, such as gravity or magnetic fields, can be used in remote sensing. Remote Sensing Technology makes use of the wide range Electro-Magnetic Spectrum (EMS) from a very short wave ‘Gamma ray’ to a very long wave ‘Radio wave’.

Interactions between Matter and Electro-Magnetic Radiation When electro-magnetic energy is incident on any given earth surface feature, three fundamental energy interactions with the feature are possible. This is illustrated in Figure 2, taking the example of an element of the volume of a water body. Various fractions of the energy incident on the element are reflected, absorbed, and/or transmitted. Applying the principle of the conservation of energy, we can state the interrelationship between these three energy interactions as shown below.

Figure 1 The Electromagnetic Spectrum


47

Incident energy = Reflected energy + Absorbed energy + Transmitted energy

EI (λ) = ER (λ) + EA (λ) + ET (λ)

Spectral characteristics of (a) energy source, (b) atmospheric transmittance, (c) remote-sensing systems

5.1 Transmittance of the Atmosphere The sunlight's transmission through the atmosphere is affected by absorption and scattering of atmospheric molecules and aerosols. This reduction of the sunlight’s intensity is called extinction. The important point to note from Figure 3 is the interaction and the interdependence between the primary sources of electro-magnetic energy, the atmospheric windows (Table 1) through which source energy may be transmitted to and from the earth’s surface features, and the spectral sensitivity of the sensors available to detect and record the energy. One can not select the sensor to be used in any given remote-sensing task arbitrarily; one must instead consider (i) the available spectral sensitivity of the sensors, (ii) the presence or absence of atmospheric windows in the spectral range(s) in which one wishes to sense, and (iii) the source, magnitude, and spectral composition of the energy available in these ranges. Ultimately, however, the choice of spectral range of the sensor must be based on the manner in which the energy interacts with the features under investigation. It is to this last, very important, element that we now turn our attention.

E I (λ) = Incident energy E R ( λ ) = Reflected engery

E A ( λ ) = Absorbed energyE T

(λ ) = Transmitted energy

Incident energy = Reflected energy + Absorbed energy + Transmitted energy E I ( λ) = E R ( λ ) + E A ( λ ) + E T ( λ )

Figure 2 Basic interactions between electromagnetic energy and an earth f f t


48

Table 1 Atmospheric Windows Useful in Remote Sensing

ATMOSPHERIC WINDOWS

Useful in Remote Sensing 0.3 µm to 1.3 µm

1.5 µm to 1.8 µm

2.0 µm to 2.6 µm

3.0 µm to 3.6 µm

4.2 µm to 5.0 µm

8.0 µm to 14.0 µm

5.2 Spectral Reflectance Curves A graph of the spectral reflectance of an object as a function of wavelength is called a spectral reflectance curve. The configuration of spectral reflectance curves provides insight characteristics of an object and has a strong influence on the choice of wavelength region(s) in which remote-sensing data are acquired for a particular application. Figure 4 shows the typical spectral reflectance curves for three basic types of earth feature: green vegetation, soil, and water. The lines in this figure represent average reflectance curves compiled by measuring large sample features. It should be noted how distinctive the curves are for each feature. In general, the configuration of

Figure 4. Typical spectral reflectance curve for vegetation, soil and water


49

these curves is an indicator of the type and condition of the features to which they apply. Although the reflectance of individual features will vary considerably above and below the average, these curves demonstrate some fundamental points concerning spectral reflectance. 5.3 Remote Sensing of Earth Resources

Figure 5 schematically illustrates the generalised processes and elements involved in electro-magnetic remote sensing of the earth’s resources. The two basic processes involved are data acquisition and data analysis. The elements of the data acquisition process are (a) energy sources; (b) propagation of energy through the atmosphere; (c) energy interactions with the earth’s surface features; (d) re-transmission of energy through the atmosphere; (e) airborne and/or spaceborne sensors; (f) resulting in the generation of sensor data in pictorial and/or digital form, in short, we use sensors to record variations in the way the earth’s surface features reflect and emit electro-magnetic energy; (g)The data analysis process involves examining the data using various viewing and interpretation devices to analyse pictorial data and/or computers to analyse digital sensor data. Reference data on the resources being studied are required (such as soil maps and crop analysis). With the aid of the reference data, the analyst extracts information about the type, extent, location, and condition of the various resources from which the sensor data were collected; (h) This information is then compiled, generally in the form of hard copy maps and tables, or as computer files, to be merged with other ‘layers’ of information in a geographic information system. Finally, (i) the information is presented to users who apply it in their decision-making process.

5.4 The Major Components of Remote-sensing Technology

Figure 5 Electro-magnetic remote sensing of the earth’s resources

Visual

Quantitative(i)Users

(e) Sensing systems (f)Data products (g) Interpretation procedures

(h) Information products

Referencedata

Pictorial

Numerical

DATA ACQUISITION DATA ANALYSIS

( a) Sources of energy

(c)Earth’s surface features

(d) Re-transmission through the atmosphere

(b) Propagation through the atmosphere


50

1. ENERGY SOURCE (PASSIVE SYSTEM: sun, irradiance from earth’s materials; ACTIVE SYSTEM: irradiance from artificially-generated energy sources such as radar)

2. PLATFORMS (Vehicle to carry the sensor) (truck, aircraft, space shuttle, satellite, etc.)

3. SENSORS (Device to detect electro-magnetic radiation) (camera, scanner, etc)

4. DETECTORS (To convert electro-magnetic radiation into recorded signals) (film, silicon detectors, etc)

5. PROCESSING (Handling signal data) ( photographic, digital, etc)

6. INSTITUTIONALISATION (Organisation for execution at all stages of remote-sensing technology: international and national organisations, centres, universities, etc

Table 2 Platform Types and Observation Objects Platform Altitude Observation Remarks

geostationary satellite 36,000km fixed point observation GMS

circular orbit satellite (earth observation)

500km - 1,000km regular observation LANDSAT, SPOT, MOS, etc

space shuttle 240km - 350km irregular observation space experiment

radio - sound 100m - 100km various investigations (meteorological, etc)

high altitude jet-plane 10km -12km reconnaissance wide area investigations

low or middle altitude plane

500m - 8,000m various aero investigation surveys

helicopter 100m- 2,000m various aero investigation surveys

radio-controlled plane below 500m various aero investigation surveys

aeroplane, helicopter

hang-plane 50 - 500m various aero investigation surveys

hang-glider,paraglider

hang-balloon 800m - various investigations

cable 10 - 40m archaeological investigations

crane car 5 - 50m close range surveys

ground measurement car 0 - 30m ground truth cherry picker

5.4.1 Resolution In general, resolution is defined as the ability of an entire remote-sensing system, including lens, antennae, display, exposure, processing, and other factors, to render a sharply-defined image. Resolution of a remote-sensing system is of different types. (1) Spectral Resolution

(2) Radiometric Resolution

(3) Spatial Resolution


51

(4) Temporal Resolution

The spectral resolution of a remote sensing instrument (sensor) is determined by the band-widths of the EMR of the channels used. High spectral resolution, thus, is achieved by narrow band widths which, collectively, are likely to provide a more accurate spectral signature for discrete objects than broad band width. However, narrow-band instruments tend to acquire data with a low signal-to-noise ratio (the ratio of effective input signal to the noise level), lowering the system's radiometric resolution. This problem may be alleviated if relatively long look (or dwell) times are used during imaging. In contrast, broad-band sensors usually have good spatial and radiometric resolution. In the broader usages of spectral resolution, there are also tradeoffs between application and spectral and radiometric resolution. In remote sensing, the data from a multiple number of channels or bands, which divide the electro-magnetic radiation range from ultra violet to radio waves are called multi-channel data, multi-band data, or multi-spectral data.

Band Number

Band Range (µm)

Potential applications

1 0.45 to 0.52 coastal water mapping; soil/vegetation differentiation; deciduous/coniferous differentiation (sensitive to chlorophyll concentration); etc.

2 0.52 to 0.62 green reflectance by healthy vegetation; etc. 3 0.63 to 0.69 chlorophyll absorption for plant species differentiation; 4 0.78 to 0.90 bio-mass surveys; water body delineation; 5 1.55 to 1.75 vegetation moisture measurement; snow/cloud differentiation; 6 10.4 to 12.5 plant heat stress management; other thermal mapping; soil moisture

discrimination; 7 2.08 to 2.35 hydrothermal mapping; discrimination of mineral and rock types;

CHANNEL NUMBER

WAVE LENGTH (µm)

USES

CHANNEL 1 0.58 - 0.68 cloud delineation, weather snow and ice mapping and monitoring, etc.

CHANNEL 2 0.73 - 1.1 surface water delineation, vegetation and agriculture assessment, range surveys, etc.

CHANNEL 3 3.53- 3.93 land/water distinction, sea surface temperature, hot spot detection (forest fires and volcanic activity),etc.

CHANNEL 4 10.3 - 11.3 day/night cloud mapping, sea and land surface temperature, soil moisture, volcanic eruption, etc.

CHANNEL 5 11.5 12.5 sea surface temperature measurement, soil moisture, weather, etc.

Table 3 Spectral Band Range (µm) used in Thematic Mapper (TM) onboard Landsat's 4 and 5 sensor system and their potential application.

Table 4. Spectral Band Range (µm) used in Advance Very High Resolution Radiometer (AVHRR) sensor onboard NOAA Satellite system and their potential application.


52

Radiometric resolution is determined by the number of discrete levels into which signals may be divided. Considering the effects of varying illumination, the radiometric dynamic range of a sensor is determined by the maximum radiance value that the sensor system can experience for a given band. For example, the initial analogue voltage signal of the Landsat (1,2,3) MSS detectors is converted to digital count output ranges from 0 to 63 for a total of 64 quantizing levels. However, the maximum number of quantizing levels possible from a sensor system depends on the signal-to-noise ratio and the confidence level that can be assigned when discriminating between levels. Information contained in digital image data are expressed by bit (binary digit) per pixel, per channel. A bit is a binary number, that is 0 or 1. Let the quantization level be n, then the information in terms of bits is given by log2n (bit). In remote sensing, the quantization level is normally 6, 8 or 10 bits. For computer processing, the byte unit (1 byte =8bits; integer value 0-255; 256 grey levels) is much more convenient. Therefore, remote-sensing data will be treated as one or two byte data. • The total data volume of multi-channel data per scene is computed as:

• data volume (byte)=(line number)*(pixel number)*(channel number)*(bits)/8. Table 5 Quantization level of remote-sensing data

Sensor Satellite Level (bit) Descriptions TM LANDSAT 6 8 bits data after radiometric correction

MSS LANDSAT 8

HRV (XS) SPOT 8

HRV (PA) SPOT 6

AVHRR NOAA 10 both 10 and 16 bits’ data are available at distribution

SAR JERS-1 3 real 3 bits, imaginary 3 bits

Spatial resolution, in terms of the geometric properties of the imaging system, is usually described as the instantaneous field of view (IFOV). The IFOV is defined as the angle which corresponds to the sampling unit on the ground. The IFOV is a function of satellite orbital altitude, detector size, and the focal length of the optical system. Thus, the IFOV, when expressed in degrees or radians, is the smallest plane angle over which an instrument (e.g., a scanner) is sensitive to radiation; when expressed in linear or area units, such as metres or hectares, it is an altitude-dependent measure of the ground resolution of the scanner, in which case it is also called an ‘instantaneous viewing area’. The field of view (FOV) is defined as the maximum angle of view in which a sensor can effectively detect electro-magnetic energy. Ground resolution is the minimum detectable area or distance on the ground. In some cases, the projected area on the ground corresponding to a pixel or IFOV is also called ground resolution. Swath width (also called the total field of view [TFOV]) is the width on the ground corresponding to the FOV.


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Temporal resolution is related to the repetitive coverage of the ground coverage by the remote-sensing system. The temporal resolution of Landsat 4/5 is sixteen days. There are very few objects and/or phenomena in nature that do not change in respect to one another throughout the course of time. For many of the physical and cultural features on the landscape, there are optimal time periods during which these features may best be observed. These optimal periods might be seasonal, or could last only for a few days or weeks. In the case of some applications, the time interval at which remotely-sensed data are acquired becomes an important factor. For example, to monitor crop growth, images should be obtained at a predetermined time interval within a year’s period. However, to monitor urban growth patterns, imagery acquired at time intervals of a year or more may be appropriate. Thus, in remote sensing, a substantial number of dynamic events, such as crop growth, rangeland development, hydrologic processes, earth damage, urban change, and marine processes; may be used as key discriminants.

SATELLITE SYSTEM SOME OPTICAL SENSOR SYSTEM

LANDSAT 4/5 MSS

LANDSAT 4/5 TM

SPOT XS

NOAA AVHRR

MOS MESSR

JERS OPS VINR and SWIR

ADEOS AVNIR

IRS-1C LISS-III

IRS-1C WiFS

Temporal resolution (Revisit Cycle) (in days)

16 16 20 (nadir)

1 image/day

17 44 41 (nadir)

24 (nadir)

24 (nadir)

Fig 6. Spatial resolution

Table 7 Overview of RS Applications

Table 6 Temporal Resolutions of some

Landsat MSS (80m)SPOT XS (20m)

IRS Pan (6m)KVR (2m)

SPOT Pan (10m) Landsat TM (30m) IRS WiFS (188m) NOAA AVHRR (1.1km)

Landsat MSS (80m)SPOT XS (20m)

IRS Pan (6m)KVR (2m)

SPOT Pan (10m) Landsat TM (30m) IRS WiFS (188m) NOAA AVHRR (1.1km)


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Natural resources development and management

Type of information to be collected from RS data

Potential decisions based on information derived from RS

Water resources for hydro power and irrigation

Mapping & monitoring of rivers, lakes, reservoirs and their catchments

Investment decisions, e.g. by funding agencies

Mapping & monitoring of snow cover; seasonal runoff forecasts

Management of reservoirs

Forest resources Mapping & monitoring of existing forests

Zoning of protection forests; definition of policies on forestry, Forest Management

Mineral resources Geological mapping; prospecting of minerals, oil, gas, etc.

Investment decisions

Agriculture Land use planning Currant land use Areas requiring intervention Historical land use and land use

changes Definition of meaningful land use plans

Soil conservation Vegetation cover maps and DEMs as input to soil erosion models such as USLE

Land use planning & zoning to improve management

Mapping of areas affected by salination Improved irrigation management Monitoring of land cover changes (e.g.

deforestation of catchments) leading to watershed degradation

land use planning

Food security Regular status maps of important crops (Crop monitoring)

Early purchases on the world markets

Infrastructure development

Transport Generation of topographic base maps incl. elevation

Planning of general projects, e.g. for roads

Telecommunication Generation of DEMs Location of transmitters Tourist infrastructure

Generation of photo maps Trip planning; Investment decisions

Urban Development

Uncontrolled urban growth

Monitoring of urban areas, also with historic images

Regional development policy

Urban densification

Mapping of vacant urban lands Location of new settlements

Disaster prevention and mitigation

Type of information to be collected from RS data

Potential decisions based on information derived from RS

Landslides Tectonics and geomorphology

Hazard zonation

Vegetation maps as input to model landslide-prone areas

Hazard zonation

Mapping of abandoned agricultural lands

Identification of afforestation areas

Weather forecasts Evacuation of people in endangered areas


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Mapping of recent landslides, e.g. with SAR images

Targeting of rescue operations

Prolonged droughts Vegetation indices Food supplies Floods Mapping of flood-prone areas

from historical satellite imagery

Hazard zonation; planning of flood protection schemes

Mapping of flooded areas Targeting of rescue & relief operations

Avalanches Mapping & modelling of avalanche-prone areas

Hazard zonation

Social development and poverty alleviation

Village level participatory exercises

Generation of photo maps to support discussions

Visualisation, learning on spatial relations

Planning of large scale programmes

Generation of topographic base maps

Identification of target areas

5.5 Aerial Photograph

Figure 7 Aerial photographs of North-western part of Kathmandu valley (1992)


56

Principal point

clock

altimeterfiducial mark

camera focal length

level

Photo Number

Figure 8 Geneal characteristics of an aerial photograph

5.6 Aerial Photography The flight configuration of aerial photographs is decided so that aerial photographs are to be viewed stereoscopically to give the three dimensional images. Overlapping pair of aerial photographs creates the apparent image displacement for the same object along the flight course because the projected images on the pair of aerial photographs are taken from two slightly different locations. Relief displacement increases radically from the centre of the aerial photographs because of the central perspective projection.

The flying for aerial photographs of the terrain has been designed to meet the conditions with sixty to eighty percent forward overlap between successive frames of photographs along a straight flight strip (flight line) and twenty percent lateral (side) lap between adjacent flight strips.


57

Figure 9 Flight configuration of erial photography 5.6.1 Scale of an Aerial Photograph The scale of an aerial photograph is a vital piece of knowledge for your work. It is the ratio of the distance on the photograph to its actual distance on the ground. This ratio of (photo distance) : (ground distance) is the scale. It is expressed usually in three ways. Descriptive scale: The descriptive scale is in common use. It is a statement of ratio in familiar terms, such as “1 cm = 1 km”. It is awkward, however, because two different units of distance are used, one for the ground and one for the photograph. Centimeters on the photographs are related to Kilometers on the ground. Graphic scale (Linear scale): The graphic scale permits direct measurement on the photographs in a convenient unit (kilometers, meters, centimeters). There is no calculation in its use; hence it is rapid and easily used. Representative fraction scale or RF (Ratio Scale):

SID

E-LA

P

OVER-LAP

Flyi

ng h

eigh

t(C

amer

a he

ight

) (H

)H

eigh

t abo

ve th

e gr

ound

Lens Focal length (f)Lens

Ground elevation(terrain level)

Film

Scale = 1/((H)/(f))

Over-lap

Flight direction (path)

flight direction

flight direction

Aircraft with aerial camera

PHOTO 1PHOTO 2

Altit

ude

of th

e ai

rcra

ftfro

m m

ean

sea

leve

las

sho

wn

by th

e al

timet

erin

the

airc

raft

Mean sea level

FLIGHT CONFIGURATION OF AERIAL PHOTOGRAPHY


58

The representative fraction (RF) is the ratio of photographs distance to ground distance with both distances expressed in the same unit of measure. Scale = (photo distance)/(ground distance) or (PD)/(GD) or PD:GD or (1)/((GD)/(PD)) corresponds to 1: (GD)/(PD). This is the basic statement of scale for all map and photographs. It is best suited for calculations. Example on an RF is 1: 100,000, which is the same as stating “1centimeter = 1 kilometer”. Thus the RF is really the familiar descriptive scale with the confusion of two units of measure removed. 5.6.1 Scale of Aerial Photograph Related to Aerial Photography Flight Mission: The scale of an aerial photograph is determined by two factors at the moment it is snapped: 1. Height of airplane above the ground ( not the altitude of the plane) (H). 2. Focal length of the camera lens taking the photograph (f). The scale is calculated by the ratio (focal length) : (height above ground) or (F) : (H). Scale varies with the height of the camera above the surface of the datum plane (elevation at the reference plane). It follows then that the scale varies within each photograph with every elevation. A tall building will have a different scale at its base from that of its roof. However, the effect of terrain height on the photo scale is not confined to such great contrasts. 5.7 Image Interpretation 5.7.1 Elements (Keys) of Image Interpretation

Color Tone Texture Pattern Shape Size Shadow Association

Color

Color display of remote-sensing data is important for effective visual interpretation.

There are two color display methods: color composite, to generate color with multi-band data, and pseudo-color display, to assign different colors to grey scale of a single image.

Tone

The continuous gray scale varying from white to black is called tone. In panchromatic photographs, any object will reflect its unique tone according to the reflectance. For example, dry sand reflects white, while wet sand reflects black. In black and white near infrared photographs, water is black and healthy vegetation white to light gray. Tone denotes the spectral reflectance of the features.

Texture

Texture is a group of repeated small patterns. For example, homogeneous grassland exhibits a smooth texture, coniferous forest usually show a coarse texture. However, this will depend upon the scale of the photograph or image.


59

Pattern

Pattern is a regular, usually repeated, shape in respect to an object. For example, rows of houses or apartments, regularly-spaced rice fields, interchanges of highways, orchards, and so on, can provide information from unique patterns.

Shape

Specific shape of an object, as it is viewed from above, will be imaged on a vertical photograph. So, the shape from a vertical viewpoint should be known. For example, the crown of a conifer tree looks like a circle, while that of a deciduous tree has an irregular shape. Airports, factories, and so on can also be identified by shapes.

Size

A proper photo-scale (image resolution) should be selected depending on the purpose of the interpretation. The approximate size of an object can be measured by multiplying the length of the image by the inverse of the photo-scale.

Shadow

Shadow is usually a visual obstacle for image interpretation. However, shadow can also give height information about a tower, tall building, mountain ranges, and others, as well as shape information from the non-vertical perspective-such as the shape of a bridge.

Association

specific combination of elements, geographic characteristics, and configuration of the surroundings, or the context, of an object can provide the user with specific information for image interpretation.

5.8 DIGITAL IMAGE PROCESSING

Image processing is manipulation of a digital image by computer and is performed either to prepare an image for display and interpretation, or to extract information from the image.

DIGITAL IMAGE PROCESSING:

CORRECTION

RADIOMETRIC CORRECTION ATMOSPHERIC CORRECTION GEOMETRIC DISTORTIONS OF THE IMAGE GEOMETRIC CORRECTION Geometric transformation Collinearity equation Resampling equation Map projection

......

CONVERSION

IMAGE ENHANCEMENT Gray scale conversion Histogram conversion Color composite Color conversion between RGB and HSI

... FEATURE EXTRACTION SPECTRAL FEATURES Special color or tone Gradient Spectral parameter

... GEOMETRIC FEATURES Edge Linearment Shape Size

... TEXTURAL FEATURES


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Pattern Spatial frequency

Homogeneity CLASSIFICATION

Figure 10 Digital Image Processing

5.8.1 Image Enhancement

Image enhancement is conversion of the original imagery to a better understandable level in spectral quality for feature extraction or image interpretation.

1. Contrast manipulation: gray-level thresholding, level slicing and contrast stretching

2. Spatial feature manipulation: spatial filtering, edge enhancement, and Fourier analysis

3. Multi-image manipulation: Multispectral band ratioing and differencing, principal components, intensity hue saturations (IHS) colour space transformation, and decorrelation stretching

Figure 11 Image Enhancement 5.8.2 Spatial Filtering

Spatial filtering is commonly used for the following purposes.

• to restore imagery by avoiding noises • to enhance the imagery for better interpretation • to extract features such as edges and lineaments


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Highpass filter Lowpass filter Sharpens an image by averaging a small area of pixels to alter its brightness.

Smoothes an image (softens) by blending a small area of pixels together to reduce detail.

5.8. Multi-spectral / Multi-band Image

Figure 12 Multi-spectral / Multi-band Images

Band 2

Band 3

Band ...

Band n

Band 1

Band 2

Band 3

Band ...

Band n

Band 1

Day 5 Database Design and Concept


Day 6

6 DATABASE DESIGN, CONCEPT AND MANAGEMENT

6.1 Introduction

For an organization to function effectively it requires accurate and timely information. Institutions and business enterprises are dependent on effective information handling to carry on their activities and maintain their competitiveness. Data storage and management are essential to handle the information. A database is a collection of information about things and their relationships to each other. A database may consist of names and addresses. The names may themselves be categorized by other relationships, such as 'client', 'friend', or 'family'. The items to be stored in the database may also be processes or concepts. The objective in collecting and maintaining information in a database is to relate facts and situations that were previously separate. This may simply require the retrieval of facts in database.

6.2 Approaches to Database Management Systems

i. File processing approach – it is the most common approach to using a database. In this approach the data stored as one or more computer files that is accessed by the special purpose.

Figure 1 It has some serious drawbacks. a. Since each application program must directly access each data file that it uses, the

program must know the data in each file are stored. This can create considerable redundancy because the instructions to access a data file must be present in each application program. If modifications are made to the data file, these access instructions must be modified in each application program.

b. If data files can be accessed and modified by several programs and several users, then there must be some overall control over which users are given access to the database and what modifications they are permitted to make. A lack of central control can seriously degrade the integrity of the database.

ii. Database Management System (DBMS) – is comprised of a set of programs that

manipulate and maintain the data in a database. They were developed to manage the sharing of data in an orderly manner and to ensure the integrity of the database is maintained. It is an important advance over the file processing approach. A DBMS acts as a central control over all interactions between the database and the

Data file 1 Data file 2 Data file 3

Application 1

Application 2

Output 1

Output 2



application programs, which in turn interacts with the user. Application programs provide the functions that the user sees, such as inventory control transactions, order entry services or geographic analysis functions. The DBMS acts as the intermediary and supervisor. It provides data independence. The application program does not need to know how the data is physically stored. It also used to tailor the style of information presentation to different users.

Figure 2 6.3 Data Models The conceptual organization of a database is termed the data model. It can be thought of as the style of describing and manipulating the data in a database. There are three classic data models that are used to organize digital databases.

i. the hierarchical ii. the network iii. the relational

these models were first developed to handle the information needs of business community and have been adapted to a wide range of other applications. These database models or their derivatives have also been adapted for use in the GIS environment.

Some important terms frequently come in the database models are – records, fields, and keys. Record – a record can be thought of as one row in a table. In a computer-based data storage system a small group of related data items are stored together as a record. The record represents the information pertaining to a particular element or entity. Entity is an object, event or concept. The terms elements and entity are used interchangeably. Field - A record is divided into fields. Each of which contains as item of data.

Key – a record is retrieved from the data file by means of key. It is a label comprised of one or more fields. Fields that are not designated as key fields are termed attribute fields. The hierarchical data model – the data are organized in a tree structure. The top of the hierarchy is termed the root. It is comprised of one entity. Every element has one higher-level element related to it, termed its parent, and one or more subordinate elements termed children. The parent children relationships can be seen in the data structure.

Data file 1 Data file 2 Data file 3

DBMS

Application 1

Application 2

Output 1

Output 2



Figure 3 The network data model- in this model one entity can have multiple parent as well as multiple child relations and no root is required. As a result data records can be directly searched without traversing the entire hierarchy above that record. While the network model does not allow many-to-many relations, this relation can be handled indirectly by using an intermediate relation, often termed an intersection record.

Figure 3 Relational data model - In the relational database model there is no hierarchy of data fields within records. Every data fields can be used as a key. The data are stored as a collection of values in the form of simple records, termed tuples. Each tuples represents a fact i.e. a set of permanently related values. The tuples are grouped together in two-dimensional tables, with each table usually stored as a separate file. The table as a whole represents the relationships among all the attributes it contains and so it is often termed a relation. 6.4 Managing Spatial And Attribute Data For GIS

Most spatial data are still being stored in the form of paper maps, imagery, tables, or text descriptions and are analyzed using manual techniques. However, there is a rapid increase in the amount of geographic information that is now being collected and stored in digital form suitable for computer-based retrieval and analysis. Many of these data sets are digital representations of conventional maps. But computer-based processing has enabled a greater

Departments

Students Professor

Courses Registration

Departments

Students Professor

Courses



range of geographic data sets, many of which are not usually represented in map form, to be accommodated within the same spatial database. When geographical data are entered into a computer the user will be most at ease if the geographical information system can accept the phenomenological data structures that he has always been accustomed to using. But computers are not organized as human minds and must be programmed to represent phenomenological structures appropriately. Most often the geographical database management system visualizes through user's perceived phenomenon structure, GIS representation of phenomenon structure, database structure and capability of hardware/software structure. 6.5 Relational Database Management System (RDBMS)







There are two fundamental approaches to the representation of the spatial component of geographic information.

i. Vector Model, and ii. Raster Model

In both model the spatial information is represented using homogeneous units. In the vector approach, the homogeneous units are the points, lines, and polygons. These homogeneous units are relatively few in number and variable in size. In raster approach, the homogeneous units are the cells. The area within a cell is not subdivided and the cell attribute applies to every location within the cell. Comparison of Raster and Vector Structure of data Raster Model Vector Model Advantages 1. it is a simple data structure 2. overlay operations are easily and

efficiently implemented 3. high spatial variability is efficiently

represented in a raster format 4. the raster format is more or less

required for efficient manipulation and enhancement of digital images

Disadvantages 1. the raster data structure is less

compact. Data compression techniques can often overcome this problem.

2. topological relationship are more difficult to present.

3. the output of graphics is less aesthetically pleasing because boundaries tend to have a blocky appearance rather than the smooth lines of hand-drawn maps. This can be overcome by using a very large number of cells, but my result in unacceptably large files.

Advantages 1. it provides a more compact data structure than

the raster model 2. it provides efficient encoding of topology, and

as a result, more efficient implementation of operations that require topological information, such as network analysis.

3. the vector model is better suited to supporting graphics that closely approximate hand-drawn maps. Disadvantages 1. it is a more complex data structure than a

simple raster 2. overlay operations are more difficult to

implement. 3. the representation of high spatial

variability is inefficient. 4. manipulation and enhancement of digital

images cannot be effectively done in the vector domain.

Source: Stan Aronoff (1989)



GIS


Day 7 7 Data management in GIS

7.1 Database for GIS Database of a GIS is a central to overall system. Building a GIS database is typical the most

Figure 1: Databases for GIS resource consuming, about 80% of implementing cost goes on this. A GIS database can be divided into two basic types of data; spatial and non-spatial. Many different data types are encountered in GIS database e.g., picture, words, co-ordinates, and complex objects. In geographical data, the positions of object establish an implied order, which is important in many operations. We often need to work with objects that are adjacent in space, thus it helps to have those objects adjacent or close in the database. There are so many possible relationships between spatial objects that, not all can be started explicitly.

7.2 Database systems There are several system developed for database management. In the past the most common is the controlled file access. There is a chance of data redundant. An example of traditional file processing system is given below in figure 2.

GIS


Figure 2: Traditional file processing system The characteristics of traditional file processing system are: ♦ Historically familiar: Since this is a traditional type of processing, it is commonly

understood to be segregated by department.

♦ Controlled file access: Each file is maintained within a specific application, access can be

tightly controlled.

♦ Personalized procedures: Each of the applications can be customized to suit a particular

application, yield very high performance.

♦ Redundant file: Given that much of the information in an organization is of value to

several users, the maintenance of the separate files within each application is redundant.

♦ Inconsistent data: The redundancy introduced by separate maintenance may allow the

same data recorded in different places to have different values.

♦ Inflexibility: The potential for the data structure to permit rapid access on an ad-hoc basis is

restricted by the segregation of files.

♦ Limited data sharing: sharing data is difficult if applications that cross normal user

boundaries have to be custom written.

♦ Difficult standards enforcement: Segregated files do not permit the development and

enforcement of standards or conventions such as naming and documentation.

♦ Excessive program maintenance: Each new application requires that a program be written

that contains many of the same functions as other applications; this level of program

duplication reduces programmer productivity.

♦ Data dependent applications: Each segregated group of files may have different format,

structure, and access strategies which will requires application specific programing.

7.3 What is a database A database is a shared collection of interrelated data designed to meet the needs of multiple users. This may not have to be computerized. However, due to the high power and relatively low price of current technology, as well as the increasing availability of data prepared in digital format, most database are intended for computer use.

GIS


Figure 3: Interrelated data design

Figure 4: Database processing system in ideal situation.

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7.4 Database management system

(A) Hierarchical database management system

(B) Network database management system

(C) Relational database management system

(D) Object oriented database management system

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7.5 Data management In GIS data can be managed in different components, geometry of the earth feature are managed as a spatial data, attribute of geographical feature are as attribute tables or tabular database. In ArcView GIS project helps to join this features and attribute in one. Database management in GIS followed by following ways: ♦ Working with spatial database

♦ Working with tabular database

♦ Creating portable projects.

7.6 Working with spatial database

♦ Identifying, Locating, and integrating spatial data ♦ Aligning themes in a view ♦ Using metadata to document database

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7.7 Working with tabular database ♦ Identifying, locating and integrating tabular data ♦ Accessing RDBMS data

♦ Understanding ODBC and other protocol and methodology ♦ Accessing a tabular data from internet ♦ Tabular data formats Data from different format can access in ArcView. Even the data from spreadsheet can be managed in ArcView readable format. Data in tabular form are export in dBASE, INFO, text to join the table with features attribute.

7.8 Field Definition- A Case of ArcView

• Number - (decimal places) • String – (specify width) • Boolean – {true (t), or false (f)} • Date – (8 digit in format YYYYMMDD) • (Use of Hot link)

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DAY 8 8 Data analysis in GIS 8.1 Introduction

The heart of the GIS is formed by the analytical capabilities of the system. What distinguish a GIS from other information system are its spatial analysis functions. Although the data input is in general the most time-consuming part, it is the data analysis why a GIS is used. The analysis function use spatial and non-spatial attributes in the databases to answer questions about the real world. Geographic analysis allows studying real-world processes by developing and applying models. Such model illuminate underlying trends in geographic analysis can be communicated with the help of map, reports or both.

The organization of the database into map layers into map layers is not simply for reasons of organization clarity; rather it is to provide rapid access to the data elements required for geographic analysis. The objective of geographic analysis is to transform data into useful information to satisfy the requirement or objectives of decision makers at all levels of detail. An important use of analysis is the possibility of predicting what will happen in another location or at another point of time. This ability provides the opportunity to select the best possible alternative.

Before starting geographic analysis, one needs to assess the problem and establish an objective. The analysis requires step by step procedures to arrive at the conclusions.

The range of analysis procedure can be subdivided into following categories:

• Database Query • Overlay • Proximity Analysis • Network Analysis • Digital Terrain Model • Statistical and Tabular Analysis

8.2 What is Spatial Analysis?

Part of decision-making process Question and answers about something geographic

Leads to decisions that affect people Involves budgeting money and resources

GIS


Spatial query examples Where is the school? Show me the pine trees? Select the freeway.

Spatial analysis examples Where should I locate a new school? Which trees are ready to harvest? Identify some corridors for the new freeway.

8.3 Spatial Analyst Application Areas

Environment analysis Vegetation cover mapping Wildlife habitat display Hazardous-waste cleanup

Business analysis Location analysis and site selection Proximity to transportation analysis Service Centres

Social analysis Census data exploration Housing studies Disease spread prediction

Hydrological analysis Stream ordering

Agriculture analysis Forestry

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Precision farming

8.4 Difficulties of Geographic Analysis • Lots of data • Spatial relationships important bur difficult to measure • Inherent uncertainty due to scale • Many data sources • Difficult to make data sources compatible • Difficult mathematics • Quantity vs. quality questions • Multiple objective • GIS can address some (but not all) of these difficulties

8.5 Relationship of Modeling To Analysis

Decision models searches through potential alternatives to arrive at a recommendation Decision support models process raw data into forms that are directly relevant to

decision making. Data characterization models are used to develop a better understanding of a system

to aid in characterizing a problem or potential solution. 8.6 Overview Analysis Functions

• Perform database query • Perform overlay analysis • Create buffer distance and proximity analysis • 3D analysis • Network analysis • Tabular and statistical analysis

8.7 Database query

• Attribute Query an operation for selecting items for attribute database using conditions formulated by users

• Spatial Query Query by point Query by rectangle Query by circle Query by line Query by polygon

• Standard Query Language (SQL)

Boolean operations are often applied in database query The selective display and retrieval of information from a database are among the fundamental requirements of a GIS. The ability to selectively retrieve information from GIS is an important facility. Database query simply asks to see already stored information. Basically, there are two types of query most general GIS allow: viz, query by attribute and query by geometry. Map features can be retrieved on the basis of attributes. For example, show all the urban areas having population density greater than 1,000 per square kilometer. Many GIS includes sophisticated function of Relational Database Management System (RDBMS), known as

GIS


Standard Query Language (SQL), to search a GIS database. The attribute database, in general, is stored in a table (relational database model) with a unique code linked to the geometric data. This database can be searched with the specific characteristics. However, more complex queries can be made with the help of SQL. GIS can carry out number of geometric queries. The simplest application, for example, is to show the attributes of displayed objects by identifying them with a graphical cursor. There are five forms of primitive geometric queries: viz, query by point, query by rectangle, query by circle, query by line, query by polygon. A more complex query still is one that uses both geometric and attributes search criteria together. Many GIS forces the separation of the two different types of queries. However, some GIS using databases to store both geometric and attribute data allow true hybrid spatial queries. 8.8 Overlay Operations The hallmark of GIS is overlay operations. Using these operations, new spatial elements are created by overlaying of maps. There are basically two different types of overlay operations depending upon data structures: raster and vector overlay. The raster overlay is a relatively straight-forward operation and often many datasets can be combined and displayed at once, The vector overlay, however, is for more difficult and complex and involves more processing. 8.9 Logical Operators The concept of map logic can be applied during overlay. The logical operators are Boolean functions. There ate basically four type of Boolean operator: OR, AND, NOT, XOR. With the use of logical, or Boolean, operators spatial elements/ or attributes are select that fulfill a certain condition, depending on two or more other spatial elements or attributes. 8.10 Vector Overlay During vector overlay, map features and the associated attributes are integrated to produce new composite map. Logical rules can be applied to how the maps are combined. Vector overlay can be performed on different type of map feature: viz, polygon-on-polygon overlay, line-in-polygon overlay, point-on-polygon overlay.

GIS


During the process of overlay, the attribute data associated with each feature type is merged. The resulting table will contain both the attribute data. The process of overlay will depend upon the modeling approach the use needs. One might need to carry out a series of overlay procedure to arrive at the conclusion, which depends upon the criterion.

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8.11 Raster Overlay In raster overlay, the pixel or grid cell values in each map are combined using arithmetic and Boolean operators to produce a new value in the composite map. The maps can be treated as arithmetic variables and perform complex algebraic functions. The method is often descried as map algebra. The raster GIS provides the ability to perform map layers mathematically. This is particularly important, for the modeling in which various maps are combined using various mathematical functions. Conditional operators are the basic mathematical functions that are supported in GIS.

8.12 Conditional Operator Conditional operators are in use with raster overlay. This all evaluate whether a certain condition has been met. = eq ‘equal’ operator

GIS


<> ne ‘non-equal’ operator < lt ‘less than’ operator <= le ‘less than or equal’ operator

> gt ‘greater than’ operator >= ge ‘greater than or equal’ operator Many system now can handle both vector and raster data. The vector map can be easily draped on the raster maps.

8.13 Buffer Operation The operation of a buffer is a frequently used spatial operation. It is used to create zones around selected geographic objects in order to perform proximity analysis. Using this operation the characteristics of an area surrounding a specified location are evaluated. The kind of analysis is called proximity analysis and used whenever analysis required to identify surrounding geographic feature. The buffer operation will generate polygon feature type irrespective of geographic features and delineate spatial proximity. For example, what are the effects of urban areas if the road is expanded by one hundred meters, to delineate five kilometers buffer zone around the national park to prevent from grazing.

8.14 Network Analysis Network models are based on interconnecting logical components, of which most important are: ‘Nodes’ define start, end, and intersections; ‘Chain’ are line features joining nodes; and ‘Links’ join together points making up a chain. This network can be analyzed by using GIS. A simple and most apparent network analysis applications are street network analysis, traffic flow modeling, telephone cable networking, pipelines, and so on. The other obvious applications would be service center locations based on travel distance.

GIS


A basic form of network analysis is to simply extract information from a network. More complex analysis processes information in the network models to derive new information. One example of this is the classic shortest-path-between two points problem. The vector mode is most suited for network analysis as compare to raster model.

Spatial analysis operation in Arc View using Geoprocessing Wizard


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DAY 9 9 GIS data output and project implementation 9.1 Important Aspects in design of Output Maps Presenting results of the analysis is the procedure by which information from the GIS is presented in a form suitable for the user. Remember that the results of GIS are used in planning and decision-making processes. Since decision-makers and planners do not usually carry out data analysis, the information should be presented to them in such way that they are able to make sound decisions. Usually, presentation of the results of GIS is given in the form of a graphic or map.

A map is basically composed of cartographic elements and geographic features.

When you make a map you should be aware of the following important aspects in the design of output maps.

Figure1: Designing a map layout 9.2 Who is going to use them?

A map intended for school children, containing very simplified data, will be very different from one made for scientists, which should contain as much factual information as possible. On the other hand, a map made for decision-makers should leave out all detail and only present the information relevant to them.

9.3 What is their purpose?

• Multipurpose (topographic, geologic) • Single purpose (one theme) • Audience • Message

9.4 What is their content?


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• Primary content (main theme) • Secondary content (base map information) • Supportive content (legends, scale, etc) 9.5 Scale of the map?

Many GIS workers unfortunately still produce maps in A4 size, irrespective of the original scale of the input maps, since it is often most convenient to make a screen dump. Or, they let the size of the output devices determine the final map scale. The scale of the output map should, however, be based upon other considerations, such as: • The purpose of the map (for example, regional planning, or detailed design) • needs of the map user • map content • Size of the area mapped • Maximum size of the map (format) • Accuracy required 9.6 Projection of the map

The projection of the mop is of importance when working over large areas. Normally, the selected map projection is that which is also used for topographic maps in a certain country.

9.7 Accuracy

1. Positional accuracy: is it at the correct place • Accuracy of data capture • Scale of map • Equipment used

2. Thematic accuracy: is it in the correct unit? 3. Semantic accuracy: cartographically okay? 9.8 Cartographic tools and visual variables

A cartographer disposes of the following tools in representing information in a map. • The basic types of spatial data: points, lines, and areas. • Volumetrically shaped: mountain shown with hill shading • Text, for legend information, topographical information and codes of mapping units • Other symbols, such as pie graphs or bar graphs, to display statistical information within mapping units.

For conveying the relevant information about these cartographic tools, a cartographer can use several visual variables. The following visual variables are available.

9.8.1 Position

The position of the point, line, or area features is, of course, given by the information already contained in the map. However, the position of these features in itself gives plenty of information. For example: the distribution of landslides connotes the most susceptible areas. 9.8.2 Form

The form of objects is a very important variable. For example: point features, such as observation points or queries, may be represented by a geometric symbol, a specifically designed symbol, or by text.


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The form of the features is also determined by the information on the map. However, the cartographer can manipulate the forms of objects, by generalization. The form of point, line, or area features is important for reading the map: complex forms attract the eye and suggest complexity; continuous lines imply continuous boundaries; and broken lines imply uncertainty.

9.8.3 Orientation

The orientation of objects can also be manipulated to convey certain information: variation in orientation creates an impression of movement and instability. Orientation is not used very frequently. The most obvious application is the use of dip-strike symbols.

9.8.4 Texture

Texture is defined as the variation in density of the graphical elements under constant value, i.e., with the same overall grey expression. Increased density contrasts attract interest.

9.8.5 Value

The visual variable that refers to the values on a grey scale, ranging from white to black. Increasing darkness implies increasing importance. The higher the quantitative value, the darker it is represented

9.8.6 Size

The higher the value, the larger the symbol. Thicker lines are more important than thin lines.

9.8.7 Color

Visual variables of color: Hue. The wavelength of a particular color. What we mean when we refer to colors as red, green, etc. Black, white, and grey are called heels’ colors. Value (Intensity). Also called brightness. The amount of light reflected by a color. The reflectance value, by comparing the reflectance value with that on a gray scale. We can reduce the value of a color by adding black to it. Saturation. The relative pureness of the color. The degree to which a color departs from a natural gray of the same value.

9.9 What should be on a map?

• Thematic information • Topographic information • Geographical location • Legend • Title • Name of author • Year of production • North indication • Scale indication • Location of study area

9.10 GIS Output Types

• Hardcopy Map • Softcopy Screen • Electronic Module

Data output types

Data are output in one of three (3) formats: viz., soft copy, hard copy, and electronic/digital.


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Soft copy output is the format as viewed on a computer screen. This may be text or maps/images in black & white or color. Because the output is displayed on a computer screen and can be erased from the screen at any time, this type of output is regarded as non-permanent. Soft copy allows the operator to interact and to preview data before its final output. Hard copy output is a permanent means of display. The information is printed or plotted on paper, photographic film, transparencies, or similar material. Maps/images and tables are usually output in this format. Electronic output consists of computer-compatible files. Information is stored on a disk, computer compatible tape, optical disk, or any other computer storage media. Although, in general, the information can be erased, the electronic output is considered to be permanent. It is used to transfer data to another computer system, either for additional analysis or to produce hard copy output at another location.

Fig 2. Integration of GIS 9.11 Characteristics of GIS Technology

~ GIS as an Information Technology (IT) are Integrating (information as such, e.g. Internet, and production processes, e.g. DIP, Computer-aided Manufacturing, IT will change the way how information is used, and how products are being made • Decentralizing in the sense, that Factual knowledge and know-how become expressed in SW and readily available to non-specialists (e.g. Text verarbeitung, GPS) IT will change the stakeholders and their relative responsibilities in any process of production and exchange • Customizing ITs allow the industrial production of client-specific products in small numbers (e.g. Serial letters, customized maps, lean production) Generation of new products, not just automating the manufacturing of existing products!

9.12 Importance of Data in GIS

data are the fuel of GIS cost of data data are the longest - living part of most GIS

9.13 Implementing GIS


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GIS Costs Data Input 70% (Labor Intensive) Database Maintenance & Management 10% Hardware/Software 10% Personnel 10% Total 100% 9.14 Spatial Data Infrastructure

9.14.1 Characteristics of Infrastructure

• IS: physical or immaterial things that can be used by individuals without having to pay the full cost of its establishment • IS are designed for multiple users, often for multiple purposes Users may or may not have to pay fees for usage e.g. telephone network, roads, statistical (census) data: cost of individual establishment is prohibitive • For an IS to work, following issues have to be resolved: • Technical Standards (e.g. on telephones) • Access, usage cost, financing. • Institutional / organizational issues (who is responsible for what) 9.15 GIS seen as an Infrastructure

Following from above, GIS in a wider sense, esp. the costly data, should be viewed as an Infrastructure. GIS as a technology will only be viable and cost-effective, if data is readily available at affordable cost. If the database has to be built from scratch for each single application, it will be too expensive and too slow for potential users. affordable cost. If the database has to be built from scratch for each single application, it will be too expensive and too slow For potential users. In this context, the term ‘Spatial Data Infrastructure’ has been coined. To sum it up: What is needed is a spatial information infrastructure which facilitates access to and responsible use of spatial data and information at an affordable cost.

Fig 3 Spatial data Infrastructure 9.16 Components of Spatial Data Infrastructures


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Note: division into technical & policy level is only indicative; sometimes seemingly technical issues become politicized, and policies are dictated by technical considerations at technical level -data as such -Metadata describing the data in terms definitions, accuracy, age, lineage, copyright, -Standards Standards are basically agreements on how things should be. When starting up spatial data Standards, one can usually take over 80-90% from International Standards that are available (e.g. FGDC). Essentially, standards guarantee a certain quality to the user, and thus enhancing the reliability of any GIS application without having to invest much time into difficult investigations. Standards should regulate: • Accuracy • Update frequency • Compatibility • Data formats and exchange standards • Data Documentation (Metadata) -Trained staff Three main issues have to be addressed in education and training programmers on GIS: •Technical officers must become ‘agents of change’, and they must be provided with the tools to be that. •Education has to be done concurrently at all levels of hierarchy (technical, middle and high management) , and also the clients have to be educated on the new technologies •A critical mass of trained people (at least 1 0% of staff in an institution) is required • At policy level -institutional / organizational arrangements -Access and Use Access: •How to find existing info in the first place (technical)? •Who will get access to the SDI? Security / political considerations? ‘Freedom of information’ or restricted Government property? •Use: Infringement on privacy rights? -Copyright and Liability Copyright: • Technically relatively difficult to enforce on data • What about derived / ‘value-added’ products? viz Graph Cassettari Liability for wrong / incomplete information: • E.g. ship wreckage because of incomplete bathymetric database • Strict specifications and statements of ‘fitness for use’ required -Pricing and Financing Pricing: information is special kind of commodity: • quantify difficult to measure • Its use is not exclusive, i.e. if I sell it, I still have it • It has the character of a public good financing of the SDI: Cost-recovery or public utility?


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-Research & Development • Development of new products & services The traditional model of product development (from science through technology to the market) has become too expensive. A new, market-driven approach to science and technology is required. this means that 60-90% of total R & D expenditure will be spent in the technology sector according to market demands • In-house / externally? -Education and awareness building (of / among decision makers, potential users and general public); not training of operating staff!

to reach out to a wider public and build a critical mass of users to bridge the Gap between producers and potential users of geographic In formation

Building a database of primary GIS data is a complex technical process which requires specialists. These are often detached from the potential users and find it difficult to bring the data or the results of their analysis into a format which is useful for the users (e.g. policy makers). On the other hand, potential end-users are often unaware of the information and the analytical capacities that exist. Hence some efforts are required to carry the message outside the community of the technical people who actually deal with GIS. 9.17 Spatial Data Infrastructure at Different Levels SDIs can be perceived at different levels: project: - IS to manage a project, like account system: defined life span organisational: - for businesses, Govt. institutions to perform their functions local: - for local Govt., administration & planning; institutional issues! life span undetermined national / international for local Government, administration and planning; research, institutional issues! life span undetermined Examples: National Spatial Data Infrastructure (NSDI), European Geographic Information. Infrastructure (EGII), National Resource Information System (NRIS) The components remain essentially the same (with different weight perhaps), but time horizons will be different. Thus the balance sheet will look differently, i.e. there is more or less time for the benefits to outnumber the costs. ‘Project life cycle’: Development cooperation projects have a typical life cycle of 1 to perhaps 5, sometimes 10 years. In this time, a project has to be concluded and certain results should be achieved. However, this is somewhat incompatible with the characteristics of organizational and / local / national SDIs, namely an open life span and a heavy focus on institutional issues. Coordination is a time-consuming, often frustrating progress which is uncertain to show any tangible results. 9.18 Institutional and Organizational Considerations Institutional & organizational arrangements identify the responsibilities of the various stakeholders in a SDI, and they define the work flow (or business process) within and between organizations. They can be formalized or an informal practice, but require a certain continuity.


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It is clear that such institutional and organizational arrangements are a crucial part of any SDI, at whichever level - from project to international. Without them, the SDI will not materialize in the first place, or it will remain unused. However, the promises of IT will only be realized if its peculiarities of ITs (integrating, decentralizing, customizing) are reflected in the institutional arrangements. It is not a case of mimicking the traditional processes and stakes on the computer

What are the implications and requirements at the different levels of a SDI?

- At all Levels: Integration of producers and users.

As already mentioned, the production of GIS data still requires specialists who are often quite far away from the users. To avoid non-use, misuse and duplication spatial databases, a close cooperation between users and producers is essential. This should happen on a regular basis in an institutionalized committee, and not in an ad-hoc fashion.

National GIS Considerations Steering Committee A Policy Board Local User Representation University Representation - Coordinating Agency -Training - Database Standards and Development - Data Distribution and Archiving - Technical Advice and Hardware/Software At the Level of Organizations Traditional organizations like Government Dept. have their own cultures and often very rigid structures. The Introduction of IT, and necessary changes in the business process, will produce winners and looser, who will oppose it (Picture Berry: Human Impacts) At inter-institutional levels (local / national /international) Existing government machineries at all levels are organized in a vertical manner along sectors and structured hierarchically. Communication and cooperation between Departments is sketchy. This often leads to duplication of efforts and incompatibilities, the some old maps are being digitized over and over again by various institutions, but they do it according to different or no standards, so nothing fits together in the end. In contrary, a SDI is a horizontal (cross-sectoral) thing, its creation and use requires a joint effort, a lot of communication and cooperation between institutions is needed. At national level, it can be accomplished by establishing a steering committee at the policy level and a coordinating agency or better: a coordinating inter-agency - committee at the technical level. In both bodies, the users should be represented prominently. 9.19 GIS Project Implementation 9.20 GIS System Development Phases


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• Inception Phase • Planning Phase • Implementation Phase 9.20.1 Inception Phase

Awareness raising, esp. among management • Pilot project: think big, start small; helps to raise awareness and generate some Know-how, can be done at low-cost • Selection of a ‘champion’ or leader for the project • Team building 9.20.2 Planning Phase

Careful planning is crucial and decisive! Viz. chart Cassettari User Requirements Analysis and Data Definition: start from the products the users need to generate (including new products in future!!), then work backwards to identify the intermediate and base data sets which are required in the process Data Dictionary: a careful definition of all required data, including their accuracies, must be made and summarized in a Data Dictionary. Remember that data are the most expensive and longest living part of a GIS! Identify the application models required to prepare the products: Can they be composed from standard GIS functions, or is programming required? Business plan (timing, funding, staffing: how to avoid ‘brain drain’?, operation) and management arrangements, e.g. work flow definition: opportunity to restructure, but don’t overload the cart because of resistance! Software/Hardware evaluation, benchmarking:

Implementation Phase

• staffing & training • installation of HW & SW • Database construction (or purchase) • application model implementation (programming, perhaps at earlier stage) Outlook: GIS Trends

GIS Technology Trends

Computer Technology

Distributed Computing Client-Server Architecture Multitasking Capability - High Quality Graphics 3-D or Topographic modeling - Network Environment Network Transparency


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- Graphical User Interface User-friendly Software Usability Engineering Database Management Technology Relational Database management System Object oriented database management technology Spatial Modeling Powerful Software Tools Spatial Database Management Artificial Intelligence Neural Networks Expert Systems Implementation Phase • staffing & training • installation of HW & SW • Database construction (or purchase) • application model implementation (programming, perhaps at earlier stage) GIS Technology Trends Satellite Technology Remote Sensing RADAR Satellite Global Positioning System (GPS) Integration of 3s - Technologies (GIS, RS, GPS) Scanning Technology Communication Technology Internet High Speed Modem Multimedia Technology Audio/Video CD/ROM Printing Technology True Color Printing Capability Social trends: GIS moving from the domain of scientists and computer freaks to the public and commercial mainstream; e.g. marketing Data is becoming a commodity with a price, but increasing amounts of data are also being put into the public domain.

Documents

1 Introduction to GIS1 Introduction to GIS 1.1 What Is a GIS? A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events