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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The National Map Hydrography Viewer
For the conterminous United States, Hawaii, and the Virgin Islands, medium and high resolution NHD data are available at 1:100,000 and 1:24,000-scale, respectively. NHD data are available for Puerto Rico at 1:20,000-scale, and at 1:63,360-scale in Alaska. Users are encouraged to work with their state's principal steward to produce and submit data...
Image: USGS Topographer at Work
The distances vary. A degree, minute, or second of latitude remains fairly constant from the equator to the poles; however a degree, minute, or second of longitude can vary greatly as one approaches the poles (because of the convergence of the meridians). At 38 degrees North latitude: One degree of latitude equals approximately 364,000 feet (69...
Image: USGS Topographers at Work
Within the conterminous 48 states, the North American Datum of 1927 (NAD 27) to the North American Datum of 1983 (NAD 83) shift of the latitude/longitude graticule (lines showing parallels of latitude and meridians of longitude for the earth) is in the range of 10-100 ground meters. Changes to UTM values are generally larger, around 200 meters,...
Image shows a scientific instrument on the slopes of Mount St Helens
The State Plane Coordinate System (SPCS), which is only used in the United States, is a plane coordinate system (north-south and east-west lines are perpendicular) in which each individual state has between one to six zones, depending on the state's size and shape. This coordinate system’s high level of accuracy is achieved through the use of...
Image: Bryce Canyon Benchmark
Most survey marks were set by the U.S. Coast & Geodetic Survey (now called the National Geodetic Survey); information for those marks is available online. For further assistance, contact the National Geodetic Survey at 301-713-3242 or ngs.infocenter@noaa.gov.  For information about marks set by the USGS, contact the National Geospatial...
Mercator the Man
The UTM (Universal Transverse Mercator) coordinate system divides the world into sixty north-south zones, each 6 degrees of longitude wide. UTM zones are numbered consecutively beginning with Zone 1, which includes the westernmost point of Alaska, and progress eastward to Zone 19, which includes Maine. If UTM ticks are shown on a USGS topographic...
Mercator the Man
The method used to portray a part of the spherical Earth on a flat surface, whether a paper map or a computer screen, is called a map projection. No flat map can rival a globe in truly representing the surface of the entire Earth, so every flat map misrepresents the surface of the Earth in some way. A flat map can show one or more--but never all--...
Image: USGS Aerial Photography and Imagery Library
Scans of traditional aerial photography film products (air photos) are not georectified. The USGS does, however, offer several orthoimagery (georectified aerial photograph) products: Digital Orthophoto Quadrangle (DOQ) High Resolution Orthoimagery (HRO) National Agriculture Imagery Program (NAIP, NAIP Plus) NAIP orthoimagery has been collected for...
Aldo Leopold Wilderness Research Institute
Paper copies of all U.S. Forest Service maps--including Forest Visitor Maps, National Forest Atlases, and Wilderness Maps--are sold through the online USGS Store, though they might not always be in stock. Paper maps are also available for purchase at some Forest Service offices and at some retail outlets. Order paper maps for individual national...
Screenshot of map corner showing two grid lines and their UTM coordinates
The Universal Transverse Mercator (UTM) grid is not used on the Forest Service Visitor Map series because of the maps’ small scale and intended use. The more detailed Wilderness maps and Special Area maps published by the Forest Service might have UTM grid ticks. UTM grids are included on all US Topo maps (7.5-minute, 1:24,000-scale) published by...
A hiker on the Lower White River Wilderness trail. BLM photo.
U.S. Forest Service Visitor maps are best used to view an entire National Forest. They are great for driving through or planning a trip to the forest  and for showing recreational sites, campgrounds, public information sites, and other attractions in the forest. Forest Service Wilderness maps are topographic maps that show natural features such as...
Florida National Scenic Trails Maps
U.S. Forest Service Visitor Maps are at a smaller scale (they show a larger area but less detail) than standard 7.5-minute (1:24,000-scale) USGS topographic maps. Unlike USGS topographic maps, Forest Service Visitor maps typically do not show elevation contours. U.S. Forest Service Visitor Maps include recreational information about camping,...