Frequently Asked Questions

Mapping, Remote Sensing, and Geospatial Data

The USGS provides the mapping and digital geospatial foundation for the Nation.

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Chesapeake Bay 2014 Landsat imagery
The National Map Services offers a series of composite base maps that combine layers into tile cache services with the cartographic richness of multiple data sources. The following base maps are available: USGS Topo  - combines the most current data (boundaries, geographic names, transportation, elevation, hydrography, land cover, and other themes...
Small Scale Collection USA
Vector data for small scales are from The National Map Small-Scale Collection (formerly National Atlas), while medium to large scales are comprised of The National Map themes, to include the National Hydrography Dataset (NHD) and Geographic Names Information System (GNIS) data. Other medium-to-large-scale vector features are from USGS edited...
Download client.jpg
The USGS only offers vector downloads in bulk by special request. For assistance, send an e-mail to tnm_help@usgs.gov and include your contact information, requested product, requested area, and download format.
Lidar data of the Gulf Islands, Florida
The most recently published figure of absolute vertical accuracy of the 3D Elevation Program (3DEP) DEMs within the conterminous United States, in terms of the National Standard for Spatial Data Accuracy (NSSDA) at 95% confidence level, is 3.04 meters.  It is important to note that the vertical accuracy actually varies significantly across the U.S...
excerpt of lidar imagery in Columbia Gorge
The area of coverage of any particular standard 3D Elevation Program (3DEP) DEM product is generally determined by the availability of source elevation data of similar or higher resolution. For example, the 1/3 arc-second layer is available for only portions of Alaska where higher resolution lidar or ifsar elevation sources exist. The 1/9 arc-...
Alaska IfSAR Elevation Image
All 3DEP seamless DEMs are provided in geographic coordinates (longitude and latitude) in units of decimal degrees, horizontally referenced on the North American Datum of 1983 (NAD83). All elevation values are in units of meters, typically referenced to the North American Vertical Datum of 1988 (NAVD88), although the National Geodetic Vertical...
northwest US and southwest Canada elevation
The USGS does not have specific data for current mountain peak elevations other than what was previously published in an Elevations and Distances in the United States booklet. A way to determine an approximate elevation at a specific point is to use the spot elevation tool query in The National Map Viewer or through the The National Map Elevation...
Fauquier County Groundwater Recharge
Average (or mean) county elevations are not currently available from the USGS.   You can, however, find the elevation at the center of a county using the Geographic Names Information System (GNIS): Go to the GNIS Domestic Names website. Select "Search Domestic Names" to open a query form. Type the county name in the Feature Name window. Select the...
Lidar image
Yes, lidar data are represented as a cloud of variably spaced point locations (x,y,z) of any terrestrial target reflecting the laser pulse. In addition to bare-earth, the point cloud will typically include buildings, trees, towers, and powerlines. 3DEP DEMs are raster surfaces of bare-earth elevation values sampled at uniform horizontal increments...
Example visualization of model output
If you think you’ve found an error in USGS elevation data, please send an email to tnm_help@usgs.gov.  We will add the reported information to our "Digital Elevation Model Issues" data log for further analysis and possible correction.  Spikes, pits, seam-line anomalies, and other data errors are of concern to us. We are working to correct or...
Screen shot of ScienceCache mobile application's map interface.
Yes, data from The National Map can be used in mobile applications. See instructions for Android and iOS users and step-by-step instructions for using MOBAC, the Mobile Atlas Creator, all at Using TNM Data on Mobile Devices. Learn more: The National Map - Mobile Information.
3D Lidar Point Cloud of the United States Capitol Building
The U.S. Geological Survey (USGS) is committed to making its websites accessible to all users in accordance with provisions of Section 508 of the Rehabilitation Act of 1973 (as amended in 1998). Currently, there is no technology capable of producing alternatives to dynamically generated geospatial images in The National Map viewer or download...