FAQ's about Geospatial Data

The University of New Hampshire has placed about 1,500 JPG-formatted images of historic topographic maps for New York and the New England states at http://docs.unh.edu/nhtopos/nhtopos.htm/.

Find more information about all USGS maps at the USGS Store and click on "Maps" in the left margin.

Most survey benchmarks were not established by the U.S. Geological Survey (USGS), but by the National Coast and Geodetic Survey, and are available on the web from http://www.ngs.noaa.gov ["Data sheets"]. For further assistance call 301-713-3242 or e-mail infocenter@ngs.noaa.gov.

USGS survey benchmark data is not yet available on the Internet

For Eastern U.S. vertical and horizontal control information contact USGS in Rolla, Missouri, by telephone 573-308-3500 or e-mail mcmcesic@usgs.gov.

For Western U.S. vertical and horizontal control information contact USGS in Denver, Colorado, by telephone 303-202-4400 or e-mail infoservices@usgs.gov.

There are several different sources available and dependent on the type of information you are searching for:

Digital Map Data

YES. Visit our Digital Geospatial Data Page or call 1-888-ASK-USGS for our information package on digital cartographic data.

Although the content of most National Atlas web pages is in the public domain, some pages may contain material that is copyrighted by others and used by the National Atlas with permission. You may need to obtain permission from the copyright owner for other uses. Furthermore, some non-National Atlas data, products, and information linked, or referred to, from this site may be protected under U.S. and foreign copyright laws. You may need to obtain permission from the copyright owner to acquire, use, reproduce, or distribute these materials.

Imagine walking along the beach. As you walk across the sand on the shore, your elevation stays constant. That path is drawn by one contour line. Now imagine walking from the shoreline into the ocean where the ground is below sea level. That path, which follows a different elevation than when you were walking on the shore, is drawn by a different contour line.

The distinctive characteristic of a topographic map is that the shape of the Earth's surface is shown by contour lines. These imaginary lines join points of equal elevation on the surface of the land above or below a reference surface such as mean sea level.

This can help measure depths of the ocean bottom, the height of mountains, and the steepness of slopes. But topographic maps show more than contours. These maps also include symbols that represent features such as streets, buildings, streams, and woods.

Scanned USGS topographic maps in GeoPDF format are available for download from the USGS Store.

Generally, for the conterminous United States, the North American Datum (NAD) shift amounts to about 210 meters. This shift occurs because of the change in shape of the spheroid used to define the datum. The GRS 80 spheroid (used for NAD 83) is shorter at the Equator and longer at the poles than the Clarke 1866 spheroid (which is used for NAD 27). The map collar says to move the projection just a few meters. The shift referenced in the map collar applies only to the LAT, LONG graticule on the map.

NOAA is the main source of bathymetric data for the world, and here is the site you can search for their data: http://www.ngdc.noaa.gov/mgg/bathymetry/relief.html

• About.com Geography
• Central Intelligence Agency World Factbook
• Houghton Mifflin Company Education Place
• National Geographic Xpeditions
• Perry-Castañeda Library Map Collection, The University of Texas at Austin
• University of Alabama, United States Maps

 

Please see our products page for a complete listing of the products and services included in the National Atlas.

No. The National Atlas of the United States of America® published by the USGS in 1970, is out of print. However, the Library of Congress has added the original National Atlas to its American Memory collection on the World Wide Web. See the American Memory site to browse through the earlier atlas.

Also, many maps from the 1970 edition can be purchased from the USGS. See our page on Maps from the 1970 National Atlas for more information. Used or antique book stores are possible sources for the 1970 National Atlas. Reference copies are available in many libraries.

The distances vary. A degree, minute or second of latitude remains fairly constant from the equator to the poles; however a degree, minute, or second of longitude can vary greatly as one approaches the poles (because of the convergence of the meridians). At 38 degrees North latitude, one degree of latitude equals approximately 364,000 ft (69 miles), one minute equals 6068 ft (1.15 miles), one-second equals 101 ft; one-degree of longitude equals 288,200 ft (54.6 miles), one minute equals 4800 ft (0.91 mile), and one second equals 80 ft.

A digital orthophoto quadrangle (DOQ) is a computer-generated image of an aerial photograph in which displacements caused by terrain relief and camera tilts have been removed. It combines the image characteristics of a photograph with the geometric qualities of a map.

EROS has digitized over 6.4 million frames of aerial film creating medium-resolution digital images (400dpi) and associated browse images for on-line viewing. Products can be downloaded at no cost through EarthExplorer or GloVis.

A DRG is a scanned image of a U.S. Geological Survey (USGS) topographic map. The scanned image includes all map collar information. The image inside the map neatline is georeferenced to the surface of the Earth.

DRG Fact Sheet

Both satellites and ground-based magnetometers are important for making measurements of the Earth's magnetic field. They are not redundant, but are, instead, complementary. After executing several orbits of the Earth, satellites can provide good geographical coverage for data collection. On the other hand, ground-based magnetometers are much less expensive than satellites, they are much easier to install and control than satellites, and, with an array of magnetometers, they can provide coverage from numerous locations simultaneously. Another consideration is that satellites orbit the Earth either inside or above the ionosphere, the electrically conducting part of the Earth's atmosphere. Since currents in the ionosphere contribute to the magnetic field, this means that the field measured by a satellite is somewhat different than the field measured at the surface. Finally, don't forget that it is at the surface of the Earth, where we live, that many of the effects of space weather are most important, so measurements from ground-based observatories will always play a critical role in space-weather studies.

Everybody. The USGS' BRD research and information is in the public domain. It's available through the Internet on the National Biological Information Infrastructure (NBII) at http://www.nbii.gov/.

The National Atlas Map Maker can be used to locate named places within the United States. Go to the Map Maker, click on the Find tab, then follow the onscreen directions.

Digital elevation model (DEM) data are arrays of regularly spaced elevation values referenced horizontally either to a Universal Transverse Mercator (UTM) projection or to a geographic coordinate system. The grid cells are spaced at regular intervals along south to north profiles that are ordered from west to east. The U.S. Geological Survey (USGS) produces five primary types of elevation data: 7.5-minute DEM, 30-minute DEM, 1-degree DEM, 7.5-minute Alaska DEM, and 15-minute Alaska DEM.

Part of a 7.5-minute DEM plot of Tumwater,Wash.

Similar digital elevation data, arranged not by quadrangles but as a huge, single, seamless file, are known as National Elevation Data, or NED. See the fact sheet available at erg.usgs.gov/isb/pubs/factsheets/fs14899.html.

Yes, GNIS actively seeks names of features that no longer exist. There are more than 100,000 such entries in the database now. To search for them, type the word "(historical)" (along with other name words if desired) in the name field. It is advisable to narrow the search further by selecting State, County, and/or Feature Class. For performance reasons, the query returns only results sets less than 2000 records.

The database also contains many historical names for features that still exist, which are termed variant names. Each geographic feature may have only one official name, but may list numerous variants. The feature query returns all features with the official name or variants matching the query, but only the official name displays in the results list. If a feature appears in the results list with a name different than the name entered, click on the name to view the feature details. The name entered will be listed among the variants. If you do not wish to query by variant names, click the Exclude Variant box under the Name field in the query page. Click the title of the Feature Name field for additional information.

The Geographic Names fact sheet is available at: http://pubs.usgs.gov/fs/2009/3016/.