Global Sources
- WorldGrids.org (public repository of environmental layers; ISRIC)
- Natural Earth (base map data for small cartographic scale maps)
- CGIAR-CSI (global data for elevation (SRTM), climate, etc.)
United Nations
National Sources
USGS
- Earth Explorer (satellite data for around the world)
- National Map Viewer (elevation grids, land cover, satellite imagery of the USA)
- EROS Data Repository (a catalog of data available at the sites above)
- The National Map (full collection of USGS mapping services)
USDA
- NRCS Geospatial Data Gateway (Soil Survey data, plus some census and watershed layers for the USA)
- NASS Cropland Data Layers
Other U.S. Federal Government Agencies
- Data.gov – geospatial (U.S. Federal Government’s data repository, filtered by geospatial data)
- Fish & Wildlife Service Geospatial Services
- National Park Service GIS links
- Environmental Protection Agency
- NOAA Hydrologic GIS data sets
- NOAA Coastal Services Center
- U.S. Census TIGER
- National Historical GIS (aggregate census data)
State Sources
- Geospatial and attribute links from the U of Arkansas
- MSU library: Geography Resources
- Michigan Center for Geographic Information
Data Clearinghouses
- Free GIS Data (from rtwilson)
- GeoCommunity’s GIS Data Depot