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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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...
Lidar image of Pittsburgh
Light Detection and Ranging (lidar) is a technology used to create high-resolution models of ground elevation with a vertical accuracy of 10 centimeters (4 inches). Lidar equipment, which includes a laser scanner, a Global Positioning System (GPS), and an Inertial Navigation System (INS), is typically mounted on a small aircraft. The laser scanner...
Aerial photo of Anvil Lake
Yes, there is a plan to scan and digitize all rolls of film. The plan is to first scan all rolls of film that are in danger of decay from vinegar syndrome and then scan everything else. Science and customer requirements are also reviewed on a regular basis, but a formal, online schedule is not available. Learn more: USGS EROS products overview...
USGS air photo of the Mud Creek landslide, taken on May 27, 2017
The U.S. Geological Survey (USGS) Earth Resources Observation and Science Center (EROS) can only certify that the product downloaded through our website is an authentic reproduction of an official record of the government that is in the legal custody of the USGS EROS. See the standard Authenticity of Digital Imagery document.
Orthoimagery of the Maryland State House, Annapolis, Maryland
The ability to see specific items in an aerial image is mostly a function of scale and resolution. The following aerial photography products all have a resolution of 1 meter or better, so you should be able to see an object the size of a house:  High Resolution Orthoimagery (HRO) National Agriculture Imagery Program (NAIP) imagery Digital...
PASA.Landsat image - Great Salt Desert - Iran - small and cropped.jpg
Many image processing programs (ERDAS IMAGINE®, PCI Geomatica®, ENVI®, IDRISI®, etc.)* can import a variety of image formats, including the GeoTIFF files of Landsat data. Free Multispec software that is included with the USGS lesson plan Tracking Change Over Time can be used for limited spectral analysis. To view Landsat scenes without using...
Example of Scan Mirror Anomaly in Landsat 7 ETM+ browse image.
A number of artifacts and anomalies can happen to any remote sensing data. Banding, dropped scan lines, and detector failures are only a few of the anomalies that can be seen in Landsat data. Go to Landsat Known Issues for details about anomalies that have been discovered and investigated.