A historical geographic information system (also written as historical GIS or HGIS) is a geographic information system that may display, store and analyze data of past geographies and track changes in time.
Historical geographic information systems are built from a variety of sources and techniques.
An especially prominent method is the digitization and georeferencing of historical maps.
This facilitates comparison of different map layers showing the geography at different times.
Comparisons between statistical areas can require reconstructing former political boundaries and other types of borders and tracking their evolution.