Thematic Data Resources
Thematic map data are typically the most difficult data type to find in digital format. In large part this is because the demand for digitization of analog thematic maps to digital formats lags behind the demand for the transition of other data types. Nonetheless, availability of high-quality digital thematic data is increasing yearly, as is the availability of tools to find such data. Open access to thematic data is greatest in the United States, so we will focus here on sources of such data in the U.S.
International digital thematic data resources can be a challenge to find, and we have not attempted to provide sources for individual countries. The company Eastview Cartographic is an excellent source specializing in GIS raster and vector data for countries worldwide.
US National Data Resources
Most thematic data are available on a (state level; there are, however, a few resources that provide nation-wide data or search capability for data on a national scale.
National Geologic Map Database
The National Geologic Map Database is an excellent resource for finding published geologic maps across the United States. The entire map catalog of the United States Geological Survey is searchable through the database, as are most geologic maps published by state geological surveys. Many maps published by societies (e.g., the Geological Society of America) are searchable in the database, as are many thesis maps.
Searches in the National Geologic Map Database can be done by latitude/longitude, place name, quadrangle name, state, and county. Options to specify particular types of maps (bedrock, surficial, geochemical) are available, as are options to limit search results to a particular scale (e.g., greater than 1:100,000) or to a particular format (e.g., digital only). A Google Earth compatible search of the National Geologic Map Database is available on a trial basis for several western states.
Digital versions of USGS geologic maps can be directly downloaded from the National Geologic Map Database. Older paper maps are frequently available as MrSID format images, some of which are georeferenced. The National Geologic Map Database provides a help page for working with MrSID map images, including a georeferencing tutorial for users of ArcGIS to illustrate how to georeference these map images.
Newer USGS digital geologic maps are typically available as ArcGIS coverages, shapefiles, or geodatabases, which can be directly imported into GIS software.
For digital maps published by state geological surveys, the database often contains a hyperlink to a location where the digital map can be obtained. These data are commonly hosted at a state geospatial data website.
The National Atlas
The map layers available through the National Atlas area an excellent source for thematic data. The National Atlas contains a broad cross section of nationally relevant data on subjects such as:
- Agricultural Data including crops, expenses, farmland
- Biological Data including land cover, forests, invasive species, animal distributions
- Public Land and Political Boundaries including Congressional districts, counties, state and federal lands
- Climate Data including precipitation data, hurricanes, sea temperature
- Environmental Data including air releases, toxic waste, hazardous materials
- Geologic Data including earthquakes, landslides, volcanoes, shaded relief
- Map Reference Data including cities and towns, urban areas, public lands
- Population Data including census, crimes, mortality
- Transportation Data including roads, railroads, and airports
- Water including streams, dams, aquifers, lakes, watersheds
United States Department of Agriculture Geospatial Gateway
The USDA Geospatial Gateway is an excellent resource for thematic data as well as topographic and remote sensing data. This Geospatial Gateway contains digital soil surveys for most of the United States, including county soil maps, soil profiles and soil reports, as well as nation-wide precipitation and temperature data. Soil maps and reports are also available on a state-by-state basis through many state geospatial data services.
US State and Local Thematic Data Resources
If you are looking for other state-specific data, try our comprehensive state-by-state listing of geospatial data sources.