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Geodatabases in GIS Engineering Geographic Information Systems CIVE 7397 Spring 09. Introduction. In ArcGIS, there are three basic data structures: shapefiles, coverages, and geodatabases.

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Geodatabases in GISEngineering Geographic Information SystemsCIVE 7397Spring 09


Introduction

In ArcGIS, there are three basic data structures:

shapefiles, coverages, and geodatabases


A geographicdata modelis a structure for organizing geospatial data so that it can be easily stored and retrieved.

Data Models

Geographic coordinates

Tabular attributes


Coverages

Developed for workstation Arc/Info ~ 1980

Complex structure, proprietary format

Attributes in Info tables

Shapefiles

Developed for ArcView ~ 1993

Simpler structure in public domain

Attributes in dBase (.dbf) tables

File-based Data Models

Geographic coordinates and attributes

are stored in separate but linked files

Arc

Info


Storing Data

Texas

Texas

Counties

Counties.shp

Counties.shx

Counties.dbf

Evap

Evap.shp

Evap.shx

Evap.dbf

Info

Coverages

Shapefiles


Coverages and Shapefiles

Coverages are stored partially in their own folder and partially in the common INFO folder. Shapefiles are stored in three to five files (with extensions .shp, .shx, .dbf, .sbx and .sbn)

Coverages store common boundaries between polygons only once, to avoid redundancy. Shapefiles store all the geometry of each polygon regardless of redundancy

Coverage features are single lines or single polygons. Shapefiles allow features to have multiple, disconnected, intersecting and overlapping components

Storing Data - Cont’d


Geodatabase and Feature Dataset

  • Ageodatabaseis a relational database that stores geographic information

  • It is a data storage and management framework for storing and manipulating spatial, geographic and attribute information


Geodatabase Structure

  • Feature class: Contains geographic information of geometric type (points, polygons, and lines) and spatial reference

  • Feature datasets: A group of feature classes forms a feature dataset

  • Non spatial tables: These do not contain any spatial attributes but can be connected to tables that have spatial information

Source: ESRI


ArcGIS Geodatabase

Workspace

Geodatabase

Feature Dataset

Feature Class

Geometric

Network

Relationship

Object Class


Why the Geodatabase

  • Geodatabases can be used to manage raster datasets

  • Scalability: Can create a personal geodatabase or a geodatabase for the enterprise

  • Attributes can be easily created and maintained

  • Geometric networks can be created for path finding analysis


Anobject classis a collection of objects in tabular format that have the same behavior and the same attributes.

Object Class

An object class is a table that has a unique identifier (ObjectID)

for each record


Afeature classis a collection of geographic objects in tabular format that have the same behavior and the same attributes

Feature Class

Feature Class = Object class + spatial coordinates


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

Relationship


Relationship

Relationship between non-spatial objects

Water

Quality

Data

Water

Quality

Parameters


Relationship

Relationship between spatial and non-spatial objects

Water quality data

(non-spatial)

Measurement station

(spatial)


Populating the Geodatabase

  • The following file types can be imported into a geodatabase:

    Shapefile, Coverage, Raster, CAD, Feature class

  • The following file types can be exported from a geodatabase:

    Shapefile, Coverage, XML, Raster, Feature class


Generating New Data

  • Scanning data: Produces a raster image which can be georeferenced after scanning

  • Digitizing image

Geographic Coordinate

System

Projected Coordinate

System

Coordinate Domains


Creating a New Feature Class

  • Need to define geometry type (line, point etc), spatial reference, fields in the attribute table


Feature Class Properties

  • Need to define geometry type (line, point etc), spatial reference, fields in the attribute table


Validating the Geodatabase

  • Defining Subtypes and Domains

    • Subtype: Subset of a record within a field

    • Domain: Coded value or range domain

Streets

Pipe

Feature class

Local

Concrete

Steel

Highway

Subtypes

BLVD, RD, AVE

HWY,

FWY

Diameter

> 14 Inch

Diameter

10 – 14 Inch

Domains


Topology

  • Define spatial relationships between features

    --- Connectivity, Adjacency, Coincidence

    --- Between one or more features

  • Maintains spatial integrity by setting rules for overlapping, intersecting etc

    Examples:

    Connectivity: Streams, streets

    Adjacency: Land parcels, municipal districts

    Coincidence: Boundary


Examples of Geodatabases

City of Houston needs to design a geodatabase for transportation infrastructure development and construction of a new Metro rail.

What layers/files/tables would the geodatabase contain?

  • Highways

  • Major roads

  • Rail routes

  • Traffic Zone Analysis

  • Traffic Hot spots

  • Congested routes

  • Commute time


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