Digitized Historic Map Collections - United States
National Historical Geographic Information System The NHGIS provides, free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2013.
Historical GIS Clearinghouse and Forum The GIS clearinghouse provides a central reference point for scholars seeking to access or catalogue projects that apply geographic technologies to historical research.
USGS Historical Topographic Map Explorer
Use this interactive map to find historic topographic maps.
Digitized Historic Map Collections - California
Claremont Consortium of Colleges - City and Town Environment Exploration Land Ownership
Sonoma State University - City and Town Land Ownership Topographic
University of California, Santa Cruz - Digital Map Collection