URBDP 422 URBAN AND REGIONAL GEO-SPATIAL ANALYSIS

Lecture 3: Building a GeoDatabase; Projections

Lab Session: Exercise 3: vector analysis

Jan 14, 2014

Objectives of Lecture

-Introduce data modeling

-Introduce alternative database models

-Review elements of geodatabase

-Introduce coordinate systems and projection

Data Modeling • Conceptual Model:– Users’ view of data

• Logical Model:– Precise definition of the set of objects of interest toidentify the relationships between them including suchrelationships as “located at”, “owned by”, “is part of”.

• Physical Model:– Implementation of data model within the framework ofrelational database technology

Data Modeling

Types of database systems

–Flat files–Relational data base–Object-oriented data base

Examples of database systems

Flat file (b) Relational

(c)

object

Behavior

Components of a Data File

Overview: Data Base Management Systems (DBMS)

• Tables in which:– rows: records, observations:

• information about one occurrence of a feature – columns: fields, attributes, data element, variables

• one type of information for all features• DBMS systems differ according to how they organize

these tables.

Data Base Management Systems (DBMS) Flat File Systems

• all records and fields contained in a single (often very large) rectangular file

• one field (or a combination) designated as key field

– unique identifier for each record

used to sort file

– records identified by key value can be found quickly

Relational Data Base SystemsCharacteristics• multiple tables (‘files’), each with different record structure• tables are related by a common record identifier item (i.e.

column variable) present in both tables• relations are created on the fly without need to maintain

pointers.– relate: temporary connection between two tables– join: permanent merge of two tables into one

The idea of "object-relational" database is to organize information into the sorts of “objects" that people recognize.

Instead of "decomposing" each feature in a distinctive list of attributes, features are stored as collections of attributes and behaviors, and can be retrieved or acted upon using a feature name.

Object- Relational Data Bases

Object- Relational Data Bases

• It enables you to make the features in GIS datasets smarter by endowing them with natural behaviors and relationship among features.

• It brings a physical model closer to its logical model. The users work with objects of interests such as roads, lakes and transformers.

• It lets you implement the majority of custombehaviors without writing any code.

• All of your geographic data can be stored and centrally managed in one database - a uniform repository

Object- Relational Data Bases

Comparison of DBMS Approaches

Building a Geodatabase

Source: ESRI 2001

Geodatabase and Feature Dataset

• A geodatabase is a relational database that stores

geographic information.

• Why? To establish and store relationships based on

tabular information.

• A feature dataset is a collection of feature classes that

share the same spatial reference frame.

• Why? To establish and store relationships based on

geographic information.

Feature Class

• A feature class is a collection of geographic objects in tabular format that have the same behavior and the same attributes.

Object Class

• An object class is a collection of objects in tabular format that have the same behavior and the same attributes.

Relationship

• A relationship is an association or link between two objects in a database.

• A relationship can exist between spatial objects (features in feature classes), non-spatial objects (objects in object classes), or between spatial and non-spatial objects.

RelationshipRelationship between non-spatial objects

Water QualityData

Water Quality Parameters

Coordinate Systems

A Coordinate System is a method of locating objects on the earth's surface.

Global Plane

Global Coordinate System

The most commonly used coordinate system today is the latitude, longitude, and height system.

Latitude and Longitude

A latitude, longitude pair specifies the location of any point on the earth’s surface

Reference planes are: Equator Prime Meridian

Latitude and Longitude

Longitude meridiansPrime meridian is zero: Greenwich, U.K.

W 180 180 E

Latitude parallels equator is zero

90 N

60

60 NN Pole (90 N)

S Pole (90 S)

Measuring Latitude o

o

o

o

Latitude measures theangular distance from the equator

Because the earth is flatter at the poles,tangent must ‘move’ further to change by 1 degree, hence 1 degree of lat. is longer at poles than at the equator.

Measuring Longitude 180o

135N Pole

70West

East70 W

135 E

Prime Meridian (0 )

o

o

oo

o

Longitude measures the angular distance from the prime meridian.

Latitude and Longitude in distance on the ground

Two points on the same north-south line of longitude, and separated by one degree of latitude are 1/360 of thecircumference of the Earth (111 km)

One minute of latitude corresponds to 1.86 km (one nautical mile)

One second of latitude corresponds to about 30 m

**But these figures apply only along the Equator.Away from the equator circles of latitude gets shorter and shorter until they vanish altogether at the poles.

…so can we easily, conveniently, sensibly calculate length and area using degrees of longitude and latitude? Not really…

All three red areas are10 degrees on a side.(100 square degrees)

• All meridians have the same length, but converge at the poles.

• Lengths of parallels decrease toward the poles (from zero latitude to 90 degrees); their degrees are shorter on the ellipsoid.

•The global referencing system is a spherical coordinate system as opposed to a plane or Cartesian coordinate system.

•The critical distinction is that Cartesian coordinate can be used to measure distances, while the distances between two spherical coordinates is not constant.

•For example the actual distance between a degree measured at the equator (111.321 km) is much larger than it is near the poles (55.802 km at 60 degrees of latitude).

Global vs. Cartesian Coordinate Systems

The process of systematically transforming positions on the Earth's spherical surface to a flat map while maintaining spatial relationships.

Map Projection

Map Projection and Distortion

Geographic objects have four geometric properties one or all of which can be distorted to a greater or lesser extent depending on the projection used.

shape or angle area distance direction

We are trying to represent the space on earth on the map space.

All projections produce some distortion

Projections types and

Property Preserved• Equal area projections preserve the area of features• Conformal projections preserve the shape of small

features (good for presentations) , and show local directions (bearings) correctly

• Equidistant projections preserve distances (scale) to places from one point, or along a one or more lines

• True direction projections preserve bearings (azimuths) either locally (in which case they are also conformal) or from center of map.

Map Projections

- cylindrical projections

- conical projections

- azimuth projections

The UTM coordinate system is based on the Universal Transverse Mercator Projection.

- Earth’s surface is divided into zones 6 degrees of longitude wide. - Zones extend from 80 degrees S to 84 degrees N - Zones are 8 degrees of latitude high.

UTM zones

State plane systems were developed in order to provide local reference systems that were tied to a national datum.

In the United States, the State Plane System was developed in the 1930s and was based on the North American Datum 1927 (NAD27).

State Plane System has been superseded by the NAD-83 System, maps in NAD-27 coordinates (in feet) are still in use.

The State Plane System 1983 is based on the North American Datum 1983 (NAD83). NAD 83 coordinates are based on meters.

State Plane Coordinates

Map Projections

In ArcGIS

Map Projection Overview http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj.html

Google Search for:esri understanding map projections pdf

Web References