Why topological relationships are important in GIS?

Topology

In aGIS, spatial relationships among features are defined by topology.

In a geodatabase, you can choose whether to create topology for features. If your analysis will depend on accurately modeling spatial relationships, creating topology is essential. For example, if you are modeling a wastewater network, all the features must be connected or the results of any analysis based on your model will be flawed. Or, if you are calculating the total area for different types of land cover, gaps between land cover polygons will result in inaccurate totals.

There are three types of topology available in the geodatabase: geodatabase topology, map topology, and the topology created for a geometric network. A feature class can participate in only one topology at a time.

Geodatabase topology

A geodatabase topology is a set of rules and properties that defines the spatial relationships you want to model and preserve in your data. ArcGIS includes over 20 topology rules from which you can choose. All feature classes participating in a geodatabase topology must be in the same feature dataset.

A geodatabase topology rule applies to a particular type of spatial relationship. For example, Must Not Have Gaps is a rule that defines a spatial relationship between polygon boundaries.

To create and edit a geodatabase topology, you need an ArcEditor or ArcInfo license.

Map topology

A map topology creates temporary topological relationships among features in one or more feature classes during an edit session in ArcMap. The ArcMap topology editing tools are used to maintain these relationships while editing.

A map topology can be created and edited using ArcView, ArcEditor, or ArcInfo. You'll learn how to work with map topology in Lab 8.

Geometric network topology

In a geometric network, topological relationships are stored in the geodatabase and maintained automatically by the software. In geodatabase and map topologies, spatial relationships are not stored�they are "discovered" as needed (for example, when a feature class is edited in ArcMap). In a geometric network topology, topological relationships are established between point and line feature classes stored in the same feature dataset.