National GIS Data Sets
The data referenced below are national coverages. Some are for all fifty states, some cover only the coterminous lower 48. Pointers are to both data and metadata wherever possible.
Geodata.gov is part of the Geospatial One-Stop E-Gov initiative providing access to geospatial data and information. You can find data, make a map, share your data, or search for information on standards and activities.
The Seamless Data Distribution System (SDDS) is the ultimate location to explore and retrieve data. U.S. Geological Survey (USGS) and the EROS Data Center (EDC) are committed to providing access to geospatial data through The National Map. An approach is to provide free downloads of national base layers, as well as other geospatial data layers. These data layers include the 1 meter Digital Orthoimagery data (DOQQ) as well as the National Elevation Dataset (NED) and National Hydrography Dataset (NHD) which are also available from other sources referenced here. Please explore both the product information and the interactive maps to learn more.
National Atlas of the United States The U.S. Geological Survey and its partners began work on The National Atlas of the United States of America in 1997. The National Atlas is designed to promote greater geographic awareness through the development and delivery of products that provide easy to use, map-like views of our natural and socio-cultural landscapes. The digital data available through this site are generally in shapefile or SDTS format, and unless noted otherwise are in 1:2,000,000 scale. Much of the 1:2,000,000 USGS data originated as DLG data, but National Atlas base cartographic data sets have been revised three times in the past ten years and will be maintained on three or five year revision cycles, depending on theme.
The National Elevation Dataset (NED) is a new raster product assembled by the U.S. Geological Survey (USGS). The NED is designed to provide national elevation data in a seamless form with a consistent datum, elevation unit, and projection. Data corrections were made in the NED assembly process to minimize artifacts, permit edge matching, and fill sliver areas of missing data. The NED has a resolution of 1 arc-second (approximately 30 meters) for the conterminous United States, Hawaii, and Puerto Rico and a resolution of 2 arc-seconds for Alaska. National Elevation Dataset data sources have a variety of elevation units, horizontal datum, and map projections. In the NED assembly process, the elevation values are converted to decimal meters as a consistent unit of measure, North American Datum 1983 is consistently used as horizontal datum, and all the data are recast in a geographic projection. Older digital elevation models (DEM) produced by methods that are now obsolete have been filtered during the NED assembly process to minimize artifacts that are commonly found in data produced by these methods. Artifact removal greatly improves the quality of the slope, shaded-relief, and synthetic drainage information that can be derived from the elevation data. NED processing also includes steps to adjust values where adjacent DEM's do not match well and to fill areas of missing data between DEM's. These processing steps ensure that the NED has no void areas and artificial discontinuities have been minimized. As higher resolution or higher quality data become available, the NED is updated to incorporate the best available coverage. As the USGS's 7.5-minute and 15-minute digital elevation products near completion for the conterminous United States and Alaska respectively, NED data will soon incorporate these sources. For the small areas that are not yet covered, the lower resolution 30-minute and 1-degree USGS DEM products were interpolated to obtain values used in NED.
The National Hydrography Dataset (NHD) is a newly combined dataset that provides hydrographic data for the United States. The NHD is the culmination of recent cooperative efforts of the U.S. Environmental Protection Agency (USEPA) and the U.S. Geological Survey (USGS). It combines elements of USGS digital line graph (DLG) hydrography files and the USEPA Reach File (RF3). The NHD supersedes RF3 and DLG files by incorporating them, not by replacing them. Users of RF3 or DLG files will find the same data in a new, more flexible format. They will find that the NHD is familiar but greatly expanded and refined.The DLG files contribute a national coverage of millions of features, including water bodies such as lakes and ponds, linear water features such as streams and rivers, and also point features such as springs and wells. These files provide standardized feature types, delineation, and spatial accuracy. From RF3, the NHD acquires hydrographic sequencing, upstream and downstream navigation for modeling applications, and reach codes. The reach codes provide a way to integrate data from organizations at all levels by linking the data to this nationally consistent hydrographic network. The feature names are from the Geographic Names Information System (GNIS). The NHD provides comprehensive coverage of hydrographic data for the United States. Some of the anticipated end-user applications of the NHD are multiuse hydrographic modeling and water-quality studies of fish habitats. Although based on 1:100,000-scale data, the NHD is planned so that it can incorporate and encourage the development of the higher resolution data that many users require. The NHD can be used to promote the exchange of data between users at the national, State, and local levels. Many users will benefit from the NHD and will want to contribute to the dataset as well.
National Land Cover Dataset Derived from the early to mid-1990s Landsat Thematic Mapper satellite data, the National Land Cover Data (NLCD) is a 21-class land cover classification scheme applied consistently over the United States. The spatial resolution of the data is 30 meters and mapped in the Albers Conic Equal Area projection, NAD 83. The NLCD are provided on a state-by-state basis. The state data sets were cut out from larger "regional" data sets that are mosaics of Landsat TM scenes. At this time, all of the NLCD state files are available for free download as 8-bit binary files and some states are also available on CD-ROM as a Geo-TIFF. The TM multi-band mosaics were processed using an unsupervised clustering algorithm. Both leaves-off and leaves-on data sets were analyzed. The resulting clusters were then labeled using aerial photography and ground observations. Clusters that represented more than one land cover category were also identified and, using various ancillary data sets, models developed to split the confused clusters into the correct land cover categories. A hierarchical land cover classification scheme of 21 classes was developed and applied in a consistent manner across the entire United States. More information is available at the site.
The Multi-Resolution Land Characteristics (MRLC) Consortium was originally formed in 1992 in order to meet the needs of several federal agencies (USGS, EPA, NOAA, and USFS) for Landsat 5 imagery, and land-cover information. The on-going need for current Landsat 7 data, land-cover and other geospatial data within the federal government culminated in reforming the MRLC Consortium in 2000 (called MRLC 2000).
USGS/National Biological Information Infrastructure (NBII)
GAP Analysis Program GAP has collaborated with many other organizations,including other federal government agencies, state and local governments, academic institutions, non-profits, and private businesses to provide regional assessments of the conservation status of native vertebrate species and natural land cover types.
USGS Water Resources Division GIS Data There is some overlap between the content of the data being served through the National Atlas and the Water Resources Division. The files on this site, however, are generally in Arc/Info export format. Again, data is 1:2,000,000 unless otherwise noted and may be of older vintage.
Census Bureau Cartographic Information These boundary files and other mapping resources are selected extracts from TIGER. They have been developed for various internal Census Bureau projects and have been made available on the Internet on an "as is" basis for the general public. They are generally in Arc/Info export or shapefile format.
The data originates from the TIGER data (mostly TIGER/line `95) and dates to the 1990 census. Scales on the TIGER data may be as precise as 1:24,000, but a number of the files that provide national coverage contain thinned data, and have been grouped in such as way that they are no longer that accurate. National coverages are probably better than the 1:2,000,000 referenced for the other data above, but can be easily combined with that data.
Bureau of Transportation Statistics The geospatial data sets distributed by the Bureau of Transportation Statistics depict transportation facilities, networks, and services of national significance. Databases are designed to be used with Geographic Information System (GIS) software packages to locate transportation features and provide a framework for transportation network analysis.