In addition to the GIS data types, features and rasters often participate in relationships with other features and with attribute values held across multiple tables. These spatial and attribute relationships, as well as certain behaviors, can be modeled by extending the three fundamental types of geographic information.
Here are a few examples of spatial and attribute relationships.
Some linear features are connected. For example, street segments connect in a road network, pipes connect in a water network, stream lines connect in a hydro network, and electrical lines connect in an electrical network. Networks can be traced, for example, to find the fastest travel route, to identify the valve to turn off in a water network, or to trace river flow downstream.
Many features are adjacent to one another and have coincident geometry; for example, adjacent counties, parcels, and other administrative areas share coincident edges.
Often, much of the descriptive information about features is held in separate attribute tables. Attributes from these separate attribute tables can be associated with each feature using standard relational database methods.
All types of geographic information—features, rasters, and attributes—can participate in these spatial and attribute relationships. In a GIS, such relationships are modeled using extended data types such as topologies and networks.
In addition, many types of spatial relationships can be discovered and identified by applying a series of spatial operators to the geographic objects. For example, you can create buffer zones of a given distance around features and perform a polygon overlay with another dataset to identify features that are near others in your GIS.