Geographic Information Systems (GISs) and digital maps are increasingly available to the computer-using humanities scholar. As a result, questions of data availability and validity are the more crucial. Digital maps may be stored in different formats, both as regards coordinate systems in use and the level of sophistication available for storing geographical information related to the maps. The maps themselves are often under copyright by a national survey agency and the situation in Norway is outlined. Historical sources may often contain geographic references to administrative units that are no longer valid. An example is taken from the University Museum of Antiquities in Oslo. Finally, an example is given of a project where maps from 1880 and 1910 are used in an architectural history project.