Frequently Asked Questions
Mapping, Remote Sensing, and Geospatial Data
The USGS provides the mapping and digital geospatial foundation for the Nation.
Browse Mapping, Remote Sensing, and Geospatial Data science related to:
• US Topo
Composite base maps are recached about once a year. Although data in dynamic service overlays are ideally updated quarterly, it can sometimes take up to six months. Please note that there will be times when composite base maps and dynamic service overlays are not in synchronization because of a difference in refresh cycles.
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When building a cache for a tiled base map service, file sizes for tiles increase four times with each zoom scale. The storage size required to cache data at scales larger than 1:18,000 is greater than the USGS can currently manage. For example, just to store data down to 1:18,000 requires a cache of over 39 million tiles. High-performing dynamic...
A tiled service contains cached tiles that render the map in small tile images. This allows the map to perform much faster when panning and zooming, compared to a dynamic service.
Dynamic is considered an "older" way of displaying web maps, where each feature is called from the source data and drawn separately for every pan and zoom. Tiled base...
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...
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...
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.
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...
Elevation products and their areas of availability are summarized on our 3-D Elevation (3DEP) Products and Services website. Detailed availability maps (status graphics) are updated monthly and can be viewed through several sites:
3DEP Product Availability Maps
The National Map Download Client – Click “Show” below each elevation product ...
Projection: 3DEP DEMS have different projections/coordinate systems depending on the product:
1/3-, 1-, and 2-arc-second (also the discontinued 1/9-arc-second) DEMs are not projected. They are all in geographic coordinates (latitude/longitude).
5-meter DEMs (Alaska only) are Alaska Albers Equal Area.
1-meter DEMs are in Universal Transverse...
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...
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...
Light detection and ranging (lidar) data are collected from aircraft using sensors that detect the reflections of a pulsed laser beam. The reflections are recorded as millions of individual points, collectively called a “point cloud,” that represent the 3D positions of objects on the surface including buildings, vegetation, and the ground. ...