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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Multi-temporal Landsat NDVI (Normalized Difference Vegetation Index) product overlaid on aerial photographs
The Spectral Characteristics Viewer is an interactive tool that can be used to visualize how the bands--or channels--of different satellite sensors measure the intensity of the many wavelengths (colors) of light. This is also known as the relative spectral response (RSR). By overlaying the spectral curves from different features (spectra), one can...
Moving Declination graphic
At most places on the Earth's surface, the compass doesn't point exactly toward geographic north. The deviation of the compass from true north is an angle called "declination" (or "magnetic declination"). It is a quantity that has been a nuisance to navigators for centuries, especially since it varies with both geographic location and time. It...
map series and scales
Simply defined, scale can be expressed as the ratio or proportion between a distance on the aerial photographs (or maps) and the actual distance on the ground or land surface. It is a ratio that could represent any unit of measurement and this ratio is called the Representative Fraction (RF). A scale usually is given as a fraction or a ratio (i.e...
Updated 2015 version of Tupelo, Mississippi US Topo quadrangle with orthoimage turned on
The National High Altitude Photography (NHAP) program was initiated in 1980 and coordinated by the U.S. Geological Survey to acquire aerial photography of the 48 conterminous United States every 5 years. This interagency program was designed to eliminate duplicate efforts in various Government programs and to maximize the use of Government funds...
Image: Lens Cone Aircraft Camera
Focal length is the distance from the middle of the camera lens to the focal plane (i.e. the film). As focal length increases, image distortion decreases. The focal length is precisely measured when the camera is calibrated. Knowledge of the focal length used, along with the altitude of the photographic aircraft, makes it possible to determine the...
Thermal infrared imagery taken with drone
Color-infrared (CIR) aerial photography - often called false color photography because it renders the scene in other than the normal colors seen by the human eye - is widely used for interpretation of natural resources. Atmospheric haze does not interfere with the acquisition of the image, therefore is well suited to aerial photography. Because...
Updated 2015 version of the Green River Lakes quadrangle with orthoimage
The aerial photographs date as far back as the 1940's for the United States and its territories. Availability of specific coverage, film type, and acquisition dates vary from agency to agency. The Earth Resources Observation and Science Center (EROS) in Sioux Falls, SD has digitized over 6.4 million frames of aerial film, creating medium-...
Photo taken from the air showing Hoover Dam with a lake backed up behind it and and a river flowing away from it.
The public may download digital aerial photography products at no cost via EarthExplorer or GloVis. Customers can request a higher resolution aerial or declassified image to be scanned for a 30.00 dollars per frame service fee.  A 5.00 dollar handling charge will be applied per request.  All requests will need to be made online through...
Image: USGS Cartographer at Work
Yes, customers will need to acquire at least 2 consecutive digital images from the same roll and then create transparencies or contact prints to view them with a stereoscope. A stereoscope is a device for viewing a stereoscopic pair of separate images, depicting left-eye and right-eye views of the same scene, as a single three-dimensional image....
Image: USGS Mapper at Work
Each National Aerial Photography Program (NAPP) frame covers a 5-by-5 mile area at 1:40,000 scale. Each National High Altitude Photography (NHAP) color infrared (CIR) frame covers an 8-by-8 mile area at 1:58,000 scale. Each NHAP black-and-white (B/W) frame covers an 11-by-11 mile area at 1:80,000 scale. Each Alaska High Altitude Photography (AHAP...
Historical Aerial View of CERC's Campus
No. A photographic enlargement only appears to show more detail than a 9-by-9 inch photograph. Photographic resolution (or image resolution) deteriorates with each enlargement factor. Photographic reproduction of images from the USGS film archives ceased on September 3, 2004. For those who specifically need paper or film products, there is a list...