A collection of collections of collections of terrain features. By terrain feature is meant any natural geographical object or feature or artificial object or purposely man-altered area that can sensibly be indicated on a map as characteristic of a region. This notion is very important in terrain analysis -- this activity being primarily conceived as a military task, but applicable in any context where the location of objects or events in a geographical environment is relevant to the reasoning. See the very broad concept of geographical thing and its various specializations.