Atlas presents in maps and text complete data about the creation and all subsequent changes (dated to the day) in the size, shape, and location of every county in the fifty United States and the District of Columbia. Non-County areas also included.
Pleiades is a community-built gazetteer and graph of ancient places. It publishes authoritative information about ancient places and spaces, providing unique services for finding, displaying, and reusing that information under open license.
DARMC "makes freely available on the internet the best available materials for a Geographic Information Systems (GIS) approach to mapping and spatial analysis of the Roman and medieval worlds. DARMC allows innovative spatial and temporal analyses of all aspects of the civilizations of western Eurasia in the first 1500 years of our era, as well as the generation of original maps illustrating differing aspects of ancient and medieval civilization. A work in progress with no claim to definitiveness."