Many of the data sources covered in previous chapters contain data with a geographic component—data that is available by country, by province, by U.S. Census tract, or data that consists of observations at a single point, such as a weather station. As users of GIS know, this data can easily be displayed and analyzed in a GIS framework. The sources in this chapter specifically provide data that is useful only in the context of GIS, such as georeferenced satellite images of the earth or shapefiles of points and polygons that can be interpreted only by GIS software. Thus, if you are helping patrons who wish to do spatial analyses, it is often necessary to consult both this chapter for GIS-specific data and the relevant subject chapter for more widely usable social, economic, environmental, or other data that is available by geography.
Major Sources: United States
Data.gov (U.S. General Services Administration)
This federal data catalog (www.data.gov), which is covered more fully in chapter 2, allows users to search an impressive amount of geographic data. As of the time of this writing, the National Oceanic and Atmospheric Administration (NOAA) was the largest contributor, with more than 32,000 of its spatial data sets included in the Data.gov catalog. The next largest contributor is the National States Geographic Information Council (NSGIC), a private organization whose members include staff from state, local, and federal agencies that deal with GIS data. Prior to the launch of Data.gov, NSGIC created a “GIS Inventory” site (http://gisinventory.net) that collected metadata about geographic data sets from these state and local agencies, allowing users to cross-search the data made available by all of the contributing agencies. The inclusion of the contents of this GIS Inventory in the Data.gov catalog allows users to search not just federally created geographic data but state and local geographic data as well. In addition, several states and state agencies are contributing metadata for geospatial data sets directly to Data.gov without going through the NSGIC GIS Inventory.
U.S. Geological Survey (U.S. Department of the Interior)
Although the Geological Survey (USGS) has contributed thousands of geographic data sets to Data.gov, it also hosts two of its own geospatial data portals, one with geographic data only for the United States and one that covers the world. The U.S.-only portal, The National Map (http://nationalmap.gov), primarily provides access to basic geographic data such as elevation; land cover; roads; cities and counties; locations of airports, hospitals, schools, and other types of structures; and boundaries of watersheds. Some additional data about land cover, natural hazards such as floods and wildfires, and conservation status is also available. Some data is available both as shapefiles and as geodatabases; other data can be downloaded as GeoTiffs. To access data, users draw a bounding box on a map and then select from a list of data available for their selected area. Access is not instantaneous; users must provide an e-mail address and wait anywhere from a few seconds up to two days to receive an e-mail with a link to download their selected data.
The other portal, EarthExplorer (http://earthexplorer.usgs.gov; free registration required to download data), covers the entire globe. It provides more advanced users access to many types of data, particularly a great deal of aerial photography and satellite imagery. Much of the latter was collected by satellites launched by the National Aeronautics and Space Administration (NASA), such as the Landsat satellites, and some of this data can also be accessed via NASA websites (see chapter 5).
INSPIRE Geoportal (European Union)
The INSPIRE Geoportal (http://inspire-geoportal.ec.europa.eu) provides access to hundreds of thousands of geographic data files produced by various public and private organizations in Europe. Although the sponsors of the data are European, some of the available data covers geographic areas beyond the European continent. A majority of the data sets include purely geographic or cartographic information—place names, political boundaries, elevation, base layers—but there are also hundreds of data sets on social, economic, and environmental issues. A great deal of care has been given to make the site function well in a multilingual environment. Keyword searches are automatically expanded to include synonyms in multiple languages; a multinational thesaurus, the General Multilingual Environmental Thesaurus (GEMET), is used to translate certain keywords into multiple languages, and all of the translated keywords are automatically included in the search. Once a language has been selected, a translation widget provides a machine translation of the metadata into the user’s chosen language.
Minor Sources
Center for International Earth Science Information Network (Columbia University)
The Center for International Earth Science Information Network (CEISEN) is different from most of the other sources in this chapter; it does not primarily provide base layers and other purely geographic data. Instead, it hosts programs and projects that provide GIS data in a variety of subject areas. One of these projects, the NASA Socioeconomic Data and Applications Center (SEDAC), is notable for providing GIS-formatted, gridded data sets based on various data sets collected by other organizations. Many of these are based on environmental data, including data sets on greenhouse gas emissions drawn from data from the Intergovernmental Panel on Climate Change. Other environmental data sets provide species distribution information for birds and mammals in the Americas, and amphibians globally, based on data from NatureServe. Another group of data sets, “Last of the Wild,” has gridded data about geographic areas with the most and the least amount of human impact, as measured by the Human Footprint Index and the Human Influence Index. There is also gridded data about the population of the United States based on demographic information from the U.S. Census, and about the population of the world based on data from the United Nations and country-level censuses.
National Historical Geographic Information System (Minnesota Population Center)
The National Historical Geographic Information System (NHGIS, www.nhgis.org; free registration required) is one of several excellent sources for historical demographic information for the United States run by the Minnesota Population Center. (Another, the Integrated Public Use Microdata Series, is mentioned in chapter 20.) This site allows users to download demographic, agricultural, and other data from the Decennial Census and other surveys run by the U.S. Census Bureau from 1790 to present. Crucially, the site also provides users shapefiles indicating the boundaries of states, counties, cities, ZIP codes, Census tracts, and so on as they existed at the time the data was collected, which makes it possible to use the historical data easily and accurately with GIS software.
U.S. Department of Agriculture
The U.S. Department of Agriculture (USDA) operates the Geospatial Data Gateway (http://datagateway.nrcs.usda.gov), which allows users to download spatial data for counties, states, and other regions of the United States. Although the data is distributed by the USDA, only some of the data—such as information about soils, orthophotographs that are part of the National Agricultural Imagery Program, and raster data about crops grown—is directly about agriculture. Other available data covers such topics as demographic and housing information, average precipitation and temperatures, land cover, conservation easements, and hydrography.