GIS: Other Suggested Resources
"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." Available as interactive maps and shapefiles that can be downloaded for use with GIS software.
A center within Columbia University's Earth Institute, CIESIN provides an extensive gateway to data and other information focusing on human interactions in the environment. Provides a topic search as well as subject access to spatial and tabular data sets held by CIESIN or hosted on its web site.