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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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
Specific data for current mountain peak elevations do not exist at USGS 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 Point Query Service....
Fauquier County Groundwater Recharge
Specific data for average (or mean) county elevations for the United States are not currently available from the USGS.  You can use the Geographic Names Information System (GNIS) query form to find an elevation on the centroid location of a county polygon by searching on a feature name, such as "County", with the "Civil" feature class. To get to...
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.
Data from The National Map (TNM) can be used in mobile applications through MOBAC, the Mobile Atlas Creator. MOBAC is a desktop (not mobile) application that will build local map caches of USGS TNM data for handheld devices, such as mobile Android phones, iPhones (iOS), and GPS. It works with the AlpineQuest, and TerraGo Edge applications for...
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...
Screen shot of the USGS Topo Base Map Shown in The National Map Viewer
International users should first set their Internet browser language to "English (United States)" to be able to access The National Map viewer.  Internet Explorer users might also need to clear their browser history and use Ctrl-F5 to refresh the cache. If Internet Explorer still doesn’t work, try using a different browser. Internet Explorer might...
The National Map Logo
Map services and data downloaded from The National Map are free and in the public domain. There are no restrictions; however, we request that the following acknowledgment statement of the originating agency be included in products and data derived from our map services when citing, copying, or reprinting: "Map services and data available from U.S...
TNMCorp250x250
Visit our API Examples Demos Web page for TNM services being used in other Application Program Interfaces (APIs), such as Leaflet, OpenLayers 2, Google Earth, and OpenLayers 3 Mobile. Other examples include usage of the Elevation Point Query Service (EPQS) and an Arctic Spatial Data Infrastructure (SDI) viewer.