A discussion about referencing and bringing historical maps into a GIS recently took place on the MapHist Mailing list. The thread on "Historical maps in GIS, accuracy, RMS error" starts here . It ranges from evaluations of different transformation algorithms to the question of why would we want to georeference historical maps at all and includes a pointer to the (free) MapAnalyst software for the accuracy analysis of old maps as well as to e-Perimetron, a Web based journal on History, Cartography, and Maps, which contains publications on geo-referencing historical maps.