Geodatabases in GIS Engineering Geographic Information Systems CIVE 7397 Spring 09

Introduction In ArcGIS, there are three basic data structures: shapefiles, coverages, and geodatabases

Data Models A geographic data model is a structure for organizing geospatial data so that it can be easily stored and retrieved. Geographic coordinates Tabular attributes 3

File-based Data Models Geographic coordinates and attributes are stored in separate but linked files Arc Info 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 4

Storing Data Coverages Shapefiles Texas Counties.shp Counties.shx Evap Info Counties Texas Counties.shp Counties.shx Counties.dbf Evap.shp Evap.shx Evap.dbf 5

Storing Data - Cont’d 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 6

Geodatabase and Feature Dataset A geodatabase is a relational database that stores geographic information It is a data storage and management framework for storing and manipulating spatial, geographic and attribute information 7

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 Object Class Relationship Workspace 9

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

Object Class An object class is a collection of objects in tabular format that have the same behavior and the same attributes. An object class is a table that has a unique identifier (ObjectID) for each record 11

Feature Class A feature class is a collection of geographic objects in tabular format that have the same behavior and the same attributes Feature Class = Object class + spatial coordinates 12

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 13

Relationship Relationship between non-spatial objects Water Quality Data Water Quality Parameters 14

Relationship Relationship between spatial and non-spatial objects Water quality data (non-spatial) Measurement station (spatial) 15

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

Geographic Coordinate 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