Applications of urban GIS include location and allocation of critical resources such as hospitals, study of disease outbreak patterns and crime analysis. Raster Geographic Information Systems, which store map features in raster or grid format, generalise the location of features to a regular matrix of cells. Each cell characterises the feature of interest within this area with a single value. GRID cell-based modelling uses the raster format to determine routing patterns and terrain. Each feature in this format is represented as a list of ordered x,y co-ordinates.
Computer algorithms exist that can convert data of one type to the other.
Thematic Mapping Maps in Geographic Information Systems are represented thematically. A standard topographic map will show roads, rivers, contour elevations, vegetation, human settlement patterns and other features on a single map sheet. In a GIS these features are categorised separately and stored in different map themes or overlays. For example, roads will be stored in a separate overlay. Likewise, rivers and streams will each be stored as a separate theme.