Geographic Information Systems (GISs) are an important software tool
in natural resource management, urban planning, public policy, and in
any application in which data is produced or analyzed in map form.
Maps have traditionally been considered to be passive representations of geographic space. Even with the advent of digital maps, the ability of the user to interact rapidly with the map on the screen has been limited to primarily to problems of reclassification and symbolism, as current spatial data structures do not permit local real-time modification. This is the "plane" approach to digital maps, where the user may fly over, but not interact with, the geographic representation. In contrast, with locally-modifiable spatial data structures and topology, a "boat" approach may be implemented where the user or observer is embedded in the map space and interacts with it directly. Like a person, or a boat, the set of immediate neighbouring objects is always known, and collision with one of these neighbours produces instant consequences!