One basic way to create or identify spatial relationships is through the process of spatial overlay. Spatial overlay is accomplished by joining and viewing together separate data sets that share all or part of the same area. The result of this combination is a new data set that identifies the spatial relationships. Volusia County GIS data are stored in the State Plane Coordinate System, which provides a common datum for registration of all data layers. This allows the user to view and analyze those portions of the various layers which cover the same place on the Earth.
The power of spatial overlay is illustrated by the project highlighted in the figure below. Three layers of data were used in the analysis which was designed to identify the development potential of land within the county. Polygons (enclosed areas) were assigned a rating based on vegetation type, soil type and whether they were in the 100-year floodplain. Then the three layers were combined to create a new layer which contained all the previous information. Finally, a comprehensive rating was determined by performing a weighted average of the three separate rating items. The result was a map contrasting suitable and unsuitable areas for development based on the land characteristics.