An event or situation that happens at the same time as or in connection with another. For example, ‘any map which shows the impact of having a number of resources in the same geographic area is a co-occurrence map. This was once accomplished with actual transparent overlays, but with the development of computer mapping, a summary map can be generated showing the locations where different numbers of factors are co-located’ (from the excellent Natural Resources Inventory on the Natural Resources Conservation Service website).

http://www.nrcs.usda.gov/wps/portal/nrcs/main/national/technical/nra/nri/ Natural Resources Conservation Service website.