Frequently Asked Questions

Mapping, Remote Sensing, and Geospatial Data

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

Filter Total Items: 203
Image: Aerial View of Roadbed Collapse
Map service metadata is available in The National Map Viewer by clicking on the pull-down arrow in front of each base data layer in the table of contents under ‘Overlays’. Service metadata can also be viewed through the data layer endpoints. Product-level metadata is also included with data downloaded in The National Map Download Client along with...
Image: Railroad Tracks
Boundaries: Primary sources include the U.S. Census Bureau, Bureau of Land Management (BLM), International Boundary Commission (IBC) for the Canadian boundary, and the International Boundary and Water Commission (IBWC) for the Mexican boundary. Boundaries include city, county, State, Federal lands, provinces, and territories; as well as cadastral...
AVHRR color mosaic of U.S., circa 1986
Geographically (and as a general reference), the United States of America includes all areas considered to be under the sovereignty of the United States, but does not include leased areas. On May 14, 1959, the U.S. Board on Geographic Names issued the following definitions based partially on the Alaska Omnibus Bill, which defined the Continental...
U. S. Board On Geographic Names
Federal, state, local, and non-governmental data partners continuously submit new features and edit existing features in the Geographic Names Information System (GNIS) database. Changes--potentially consisting of hundreds to thousands of records per month--are validated by the staff and made available on the GNIS website and in the Web services....
Image: Rocky Mountain National Park
The Geographic Names Information System (GNIS) was developed by the U.S.Geological Survey (USGS) in cooperation with the U.S. Board on Geographic Names (BGN), which maintains cooperative working relationships with state names authorities to standardize geographic names. GNIS contains information about the official names for places, features, and...
small excerpt of Yosemite Valley topographic map in shades of green and brown
They both might be correct. The reason that the elevations do not agree might be because they are set on different datums. Most maps use NAD27 and the elevations are based on mean sea level. Your GPS receiver uses WGS84 and the elevations are based on the NAD83 ellipsoid. These datum shifts can result in difference of tens of meters horizontal and...
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...
Color infrared aerial photo mosaic, UMRS Pool 8, 2000
Color-infrared (CIR) aerial photography--often called "false color" photography because it renders the scene in colors not normally seen by the human eye--is widely used for interpretation of natural resources. Atmospheric haze does not interfere with the acquisition of the image. Live vegetation is almost always associated with red tones. Very...
Photo taken from the air showing Hoover Dam with a lake backed up behind it and and a river flowing away from it.
Download medium-resolution scans (400 dpi) of aerial photography products at no charge using EarthExplorer. We are working on high-resolution scans (25 micron or 1,000 dpi) that can also be downloaded at no charge. With over 8.4 million frames of imagery in our archive, scanning will take many years to complete, but about 80% of high-resolution...
Image: USGS Mapper at Work
The area covered by an aerial photograph (air photo) depends on the scale of the imagery. Most air photos were taken on 9 x 9 inch film. The chart below reflects coverage for a variety of photographic scales. Scale 1 inch = feet 1 side (miles) Area (square miles) 1:12,000 1000 1.70 2.9 1:20,000 1667 2.84 8.1 1:24,000 2000 3.41 11.6 1:40,000 3333 5...