Concepts and Functions of

Geographic Information Systems(1/5)

MSc GIS - Alexander Mogollon Diaz

Department of Agronomy

2009

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Concepts and Functions of GIS

.PPT Topic #1 Topic #2 Topic #31 A GIS is an information

systemGIS is a technology

2 Spatial Data modelling Sources of data for geodatasets

Metadata

3 Geo-referencing Coordinate transformations

4 Database management

5 Spatial Analysis

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Maps

• Are the traditional instrument to describe the world as it was, is, will (probably) be, we want it to be – Topographic and thematic maps– Cadastral plans– Photo-maps, Satellite image based maps

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Map scale = 1:50.000

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Photo scale = 1:10.000

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Plan scale = 1:2.500

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Maps• Display the location and shape of entities of

the real world (geographic reality)• Describe the state of geographic reality at a

given moment in time• Give meaning to displayed entities by

symbolisation according to a map legend• Information content is related to map scale• Are static, difficult to update

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Plans / Sketches

• Plans and sketches are the traditional instruments to describe the world as we want it to be

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Plan scale = 1:2.500

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Spatial databases

• With the advent of GIS-technology, a new instrument is introduced: the spatial database

• Data describing geographic reality are no longer stored in maps, plans and sketches but in digital databases

• GIS-software provides tools to create and work with spatial databases to– produce maps …– enhance knowledge– support decisions

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From data collection to database

A/D conversion

Structuring

Computing functions

Other functions

Data collection Database Information System

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From data collection to database

Data about entities:•persons•associations•companies•licences•invoices•municipalities, districts•properties, …

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Data about entities

• Persons• Associations• Companies• Invoices• Insurance contracts• Provinces• Parcels• Buildings• ….

• Date of birth, ...• List of members, ...• List of employees, ...• Due date of payment, ...• Insured risks, ...• Capital city, ...• Owner, ...• Construction cost, ...

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Database = structured collection of digital data

• If not acquired in digital form, data need to be converted from analogue to digital form

• Structuring is required to facilitate search and query of the data:– Tables are often used to structure the data– Several software packages/tools exist to integrate data

in tables for further processing• MS-Access, MS-Excel, dBase, … are table- (row/column)

based

• Data collections contain very frequently an implicit indication of location: address, administrative/statistical unit, ...

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From database to information system

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Data about entities:•persons•associations•companies•licences•invoices•municipalities, districts•properties, …

What ?Wen ?

What if ?

From database to information system

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Information system • Database equipped with tools which allow to

ask questions and obtain answers• Information = structured and interpreted data,

fit for specific use• Information = data put in its context to allow

for interpretation• Information is derived from data using

transformation tools– query tools– computing tools– advanced analytical tools– presentation tools

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Questions about entities

• Persons• Associations• Companies• Invoices• Insurance polices• Provinces• Parcels• Buildings• ….

• How old ? When 18 ?• How many members ?• Monthly salary cost ?• Amount unpaid ?• How large the risk ?• Budget deficit ?• (Un)built ?• For students ?

What if taxes rise with 10% ?What deficit if #students decrease to 25.000 ?

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From database to information system

What ?

When ?

What if ?

WHERE ?

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Data about spatial entities•rivers, hydrography•spatial destination zones•muncipalities•properties, buildings•...

What ?When ?

What if ?WHERE ?

From maps and other collections of spatial data to GIS

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Spatial entities (1)• Cadastral entities, properties, buildings

– Patrimonium– Unbuilt parcels– Domicilies

• Entities related to spatial planning– Transport infrastructure (road, railway, public transport

connection, water- and airways,...)– Zones with a defined spatial destination– Zones with an effective land use– ...

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Spatial entities (2)

• Entities related to security policy– Location of traffic accidents– Properties where theft occurred– …

• Entities for planning of natural resources– Fossil fuel fields– Mining zones– Fishing areas– Natural reserves– UNESCO world heritage

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Spatial entities (3)• Entities related to agricultural and environmental

policies– Agricultural zones and parcels– Irrigation and drainage canals– Water abstraction points– Zones for soil erosion abatement

• Other entities– Location of wind mills– Mangrove patches– Traffic lights– Sewer lines, electricity lines

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From data on spatial entities to spatial information

• From data regarding buildings, demography, migration to requirements for housing

• From data regarding (non-) irrigated agricultural land, soils and climate to rice production capacity by province

• From data on factories and owners of cars to air quality distribution

• From data regarding beach resorts to regional touristic potential

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Spatial entities and spatial objects• Spatial entities

– Are elements of geographic reality with a clear boundary ‘crisp’ – Spatial entities of a given type are grouped into classes of spatial entities– Data about spatial entities can be implicitly spatial (adresses, other indirect

references) or explicitly spatial (coordinates)

• Incorporation in a gDB of spatially explicit data about spatial entities requires abstraction and modelling

– Spatial entities are abstracted and modelled as spatial objects– ‘Feature’ is used as a synonym for both ‘entity’ and ‘object’

• Spatial objects– Spatial objects have:

• a location expressed according to a known reference system• A geometric shape: point, line, area/polygon, volume, one or more cells (pixel), voxel

(3D-cells or cubes)• descriptive attributes (characteristics, properties, behaviour)

– Objects of the same shape-type and sharing the same attribute structure belong to one object class. Such class has most often more than one member

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An Example

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Y

X

Identification Name

6045 Land Use

   

   

6045

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Y

X

  

  

Building101

NameIdentification

101

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Y

X

  

  

99-nov-16tA0023

3

DateIdentification

A00233

30The real world = spatial entities + ??

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Terrain• Geographic reality is more than classes of spatial

entities• The spatial continuum or Terrain in which entities

occur– Elevation (shaping relief and landscapes)– Depth of lakes, aquifers– Concentration of toxic substances in soil, surface water, …– Air quality– Noise, …

• Terrain = spatially variable characteristics of individual locations

• Each terrain characteristic (e.g. elevation) is modelled as a Digitaal Terrain Model (DTM) of ‘single valued surface’ (surface)

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Data about spatial entities and/or terrain•rivers, hydrography•spatial destination zones•muncipalities•properties, buildings•elevation, bathymetry, …

What ?When ?

What if ?WHERE ?

From spatial database to GIS

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gDB contains data about spatial entities and/or terrain

• All geographic data have three components:– A geometric component: defines the position and shape of

objects/locations with respect to a reference system; ALWAYS present

– A descriptive component: attaches characteristics or attributes to objects or locations

– Time as the third component. Locations and/or characteristics can change over time

• Geographic primitive = most elementary building block for the description of the geometric component of spatial entities and terrain – Points– Cells

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Data in a gDB must be structured and interpreted

• Structuring of the geometric primitives ‘point’ or ‘cell’ – into 2D-geographic objects:

• Elementary point, line, polygon objects• More complex network, region objects• Cells and aggregations of cells• Linked to ATTRIBUTE-information

– into 2.5D surfaces (for terrain characteristics):• Relief, groundwater, noise

– into 3D-geographic objects (volumes)

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Example of geometric structuring

Y

X

Points are structured into lines which define 2D-polygons

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Example of geometric structuring

Points/cells are structured into 2.5D surfaces

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Data in a gDB must be structured and interpreted

• Interpretation of the geometric object- and surface structures through coupling with identification codes and characteristics:

– Object classes with individual members: specific parcels, water courses, land use zones, …

– Surfaces which model specific terrain characteristics (e.g. digital elevation model; digital noise intensity model)

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Geographic databases

• Database = geographic database if it contains data about:– Location– (Shape)– (Characteristics) of geographic objects and/or

about terrain-characteristics

• gDB with computing and other functions = GIS

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GI-Systems

• Are information systems; allow the user to formulate questions about geographic reality and obtain ‘best possible’ answers

• Comparable to non-spatial information systems

• Emphasis is on the geometric component, the ‘Where-question’

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Generic questions for a GIS – What is at a given location ?

• Which type of building ? How deep is the groundwater table ?

– Where are the entities with the specified characteristics ?• Where are the severely degraded zones within the province ?

– What has changed since ?• Which roads have been built since ?

– Which spatial patterns do occur ?• Which is the configuration of atmospheric high and low pressure

zones ?

– Which are the consequences of ? What if ?• Which area will flood if a dike is perforated at a given location ?

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GIS = IS GIS = TECHNOLOGY to build and exploit gDBs

Spatial data modelling

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GIS = IS GIS = TECHNOLOGY to build and exploit gDBs

ManagementTransformation

Visualisation, Query, CartographyAnalysis

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GIS as a technology

• Sets of computer programs, infrastructure and know-how

to:– A/D-convert– Structure– Process data about spatial entities and terrain into information

– Query and communicate this information • Based, to an important extent, on database-technology

(DBMS)• Applicable in each thematic domain for which locations

are important• Support of decisions

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Summary of important items • The world as it is or was; The world as we expect it or want

it to be

• Maps versus spatial databases• Spatial entities versus terrain characteristics• Nature of geographic information

• A GIS is an information system – that can provide answers to ‘where ?’ and related questions

regarding the current, past, expected and planned geographic reality – that is based on a model of the geographic reality which is captured

in a spatial database (gDB)• GIS is a technology

– which enables to build and exploit spatial models/gDB

Questions or remarks ?

Thank you …