The program comes with a large integrated gazetteer of placenames in the British Isles, collected from many different sources and optimised for historical usage. The top of this gazetteer (entries beginning A..) is shown here, as displayed in one of the program dialogues.
Placename Gazetteer dialogue
As well as a map reference, for each location the gazetteer includes both a "Search" spelling and a modern "Display" spelling, such that many historical synonyms and known spelling variants are present. All ancient parishes in Gt. Britain are covered, also many places that grew to importance after the Industrial Revolution. The database is optimised for genealogical use, including most of the places that appear in the IGI and the 1881 Census on CD-Rom. Coverage of historical Irish places is fraught with difficulties and inconsistencies of spelling, but GenMap v2.0 incudes many more Irish locations than v1.0.
See the Import Wizard page for information on how the program uses the gazetteer to identify places when importing from an external file.