PostGIS Cookbook - Second Edition

Getting ready

The basic pattern for handling geometry collections is to use ST_Dump to convert them to a dump type, extract the geometry portion of the dump, collect the geometry, and then convert this collection into a multi-polygon. The dump type is a special PostGIS type that is a combination of the geometries and an index number for the geometries. It's typical to use ST_Dump to convert from a geometry collection to a dump type and then do further processing on the data from there. Rarely is a dump object used directly, but it is typically an intermediate type of data.