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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Rendering of Landsat 9
Landsat 9—a partnership between the USGS and NASA—has a launch readiness date of mid-2021. Landsat 9 will be launched from Space Launch Complex 3E at Vandenberg Air Force Base in California and will be delivered into orbit by a United Launch Alliance Atlas V 401 launch vehicle. Learn more: Landsat 9 Mission Since 1972, Landsat satellites have...
Scanned USGS historical map of the Yorktown, Virginia area, circa 1907
Many different datums exist, but in the United States only three datums are commonly used: The North American Datum of 1927 (NAD27) uses a starting point at a base station in Meades Ranch, Kansas and the Clarke Ellipsoid to calculate the shape of the Earth.  The North American Datum of 1983 (NAD83) was developed when satellites enabled a better...
Portion of 2017 US Topo Grand Teton WY Quad Map, image layer off
On a Geographic Names Information System data query, the field "Topo Map Name" indicates the name of a standard USGS topographic map. If the map name is known and entered in this field, the query will return the names of all geographic features that are wholly or partially located on that map. Note that there might be more than one state with maps...
Image shows a satellite view of Guadalupe Mountains National Park after a wildfire
LandsatLook images are full-resolution .jpeg files that are included as options when downloading Landsat data from EarthExplorer, GloVis, or via the LandsatLook Viewer. These are useful for simple visual interpretation without the need for specialized software. LandsatLook products include: LandsatLook "Natural Color" Image (3-band composite)...
Thumbnail of a topographic map with a grid of individual indexes and their names.
View map indices on these interactive maps (you must zoom in to see the index lines and map names): Map Locator on the USGS Store - Click the icon on the left that looks like two pieces of paper and select “1:24,000”. TopoView - Click on any of the round map scale indicators on the right side of the map.  The National Map Viewer - Click on the...
Image: Cartographers in the Field
The distinctive characteristic of a topographic map is the use of elevation contour lines to show the shape of the Earth's surface. Elevation contours are imaginary lines connecting points having the same elevation on the surface of the land above or below a reference surface, which is usually mean sea level. Contours make it possible to show the...
Image: Alaskan Elders
Once you've gathered as many facts about family history and customs as possible, turn to maps to uncover more specific information or to solve historical mysteries. In the United States, birth, death, property, and some other kinds of records are normally kept by county governments. If you can name the place where an ancestor lived, new or old...
Vertical line with a star at the tip, second angled line with GN at the tip, third angled line with MN at the tip.
A diagram at the bottom of most USGS topographic maps shows three north arrows--true north, grid north, and magnetic north--and the angles between them. Some maps, especially very old maps, do not have this diagram. Example of north arrows from US Topo map. Star is True north, GN is Grid north, MN is Magnetic north. (Public domain.)   True...
1914 USGS legacy topographic map of the Muscle Shoals, Alabama
A USGS topographic map is usually named for the most prominent feature within the bounds of the map, which is frequently a community. Most topographic maps are named for the most centrally located, well-known, and/or largest community identified on the map. If the community for which the map should be named falls on two or more maps, a directional...
Crop of Landsat 7 Path 38 Row 35, Acquired March 29, 2013
Landsat 7 ETM+ SLC-off data refers to all Landsat 7 images collected after May 31, 2003, when the Scan Line Corrector (SLC) failed. These products have data gaps, but are still useful and maintain the same radiometric and geometric corrections as data collected prior to the SLC failure. See the Landsat 7 website for information about the SLC-off...
Landsat image showing scar marks from fire in comparison to ASTER.
Data acquisition requests are not available to the public. The Landsat 8 and Landsat 7 satellites each acquire data on a continual basis in accordance with their respective Long Term Acquisitions Plans. The Landsat Acquisitions page has calendars and information about daily schedules. Learn more: Landsat 8 Long Term Acquisitions Plan Landsat 7...
Image shows aerial imagery of flooding in Louisiana, courtesy of the National Geodetic Survey
Remote sensing is the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance (typically from satellite or aircraft). Special cameras collect remotely sensed images, which help researchers "sense" things about the Earth. Some examples are: Cameras on satellites and...