Frequently Asked Questions

Mapping, Remote Sensing, and Geospatial Data

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

Filter Total Items: 213
Landsat 7 Enhanced Thematic Mapper Plus (ETM+) Level-1 Data
The table below shows the Landsat Collections Level-1 processing levels: Landsat Level-1 Processing Levels Processing Level Description Terrain Precision Correction (L1TP) Radiometrically calibrated and orthorectified using ground control points (GCPs) and digital elevation model (DEM) data to correct for relief displacement.The highest quality...
Example visualization of U.S. Landsat Analysis Ready Data tile-based structure and time-series stacking.
U.S. Landsat Analysis Ready Data (ARD) are pre-packaged and pre-processed bundles of Landsat data products that make the Landsat archive more accessible and easier to analyze, and reduce the amount of time users spend on data processing for time-series analysis. ARD contains Level-2 products derived from Landsat Collections Level-1 scenes. ARD are...
Landsat 9 logo
Landsat 9 will carry the same instruments that are on the Landsat 8 satellite but with some improvements: Operational Land Imager-2 (OLI-2) for reflective band data. Thermal Infrared Sensor-2 (TIRS-2) for the thermal infrared bands. OLI-2 will have a slightly improved signal-to-noise ratio over Landsat 8's OLI. Landsat 9’s TIRS-2 is a Class...
Rendering of Landsat 9
Landsat 9—a partnership between the USGS and NASA—has a launch readiness date of September 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...
Scanned USGS historical map of the Yorktown, Virginia area, circa 1907
Many different horizontal reference 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...
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...