United States Sources

Environmental Conservation Online system (ECOS)

This site sponsored by the U.S. Fish and Wildlife Service is a gateway web site that provides access applications which manage data regarding threatened and endangered species, fisheries,and habitat conservation.

USGS Publications Warehouse

On this site you will find full text online access to publications from the USGS inlcuding research, reports and investigations. These reports are in a specialized digital format which you are required to download from the site in order to view.

National Historical Geographic Information System

The National Historical Geographic Information System (NHGIS) provides, free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2011. (excerpt from web site)