FAQ's about Maps

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.

The needle of a compass is a small magnet, one that is allowed to pivot in the horizontal plane. The needle experiences a torque from the ambient magnetic field of the Earth. The reaction to this torque is the needle's preferred alignment with the horizontal component of the geomagnetic field. The 'north' end of the compass needle is simply the north end of the magnet, and it is the end of the compass needle that points in the general direction of the geographic north pole; naturally, the 'south' end of the compass needle is the south end of the magnet and it points in the opposite direction, towards the general direction of the geographic south pole. Having said this, the preferred directionality of a compass can be affected by local perturbations in the magnetic field, like those set up by (say) a near-by electrical system; a compass can also be affected by local magnetization of the Earth's crust, particularly near large igneous or volcanic rock deposits.

Browse the following websites for more information:

• US Recent Earthquakes
• World-wide Recent Earthquakes
• World-wide Earthquakes in the Last 7 Days
• NEIC QED list
• Global Earthquake Information - IRIS Seismic Monitor
• United States - ANSS

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.

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'. It is a quantity that has been a nuisance to navigators for centuries, especially since it varies with both geographic location and time. It might surprise you to know that at very high latitudes the compass can even point south! Declination is simply a manifestation of the complexity of the geomagnetic field. The field is not perfectly symmetrical, it has non-dipolar 'ingredients', and the dipole itself is not perfectly aligned with the rotational axis of the Earth. Interestingly, if you were to stand at the north geomagnetic pole, your compass, held horizontally as usual, would not have a preference to point in any particular direction, and the same would be true if you were standing at the south geomagnetic pole. Moreover, if you were to hold your compass on its side the north-pointing end of the compass would point down at the north geomagnetic pole, and it would point up at the south geomagnetic pole. Maps of declination, such as that shown below (contours of 10 degrees east), as well as other field components, and a program for determining the magnetic field at any geographic location, are given in the Models, Charts, and Movies pages of this website.

USGS Field Records Library

Box 25046, MS 914

Denver Federal Center

Denver, CO 80225-0046

Telephone: 303-236-1000

FAX: 303-236-0015

TDD: 303-236-0998

E-mail: den_lib@usgs.gov

Jill Schneider

USGS Mineral Resources Surveys

Alaska Section

4200 University Drive

Anchorage, AK 99508-4667

Telephone: 907-786-7457 (Office) and 907-786-7007 (Library)

FAX: 907-786-7401

E-mail: jschnidr@usgs.gov

Two other sources of field records are:

1. National Archives and Records Administration (NARA) in College Park, Maryland, which keeps field record materials in their Archives II facility. Refer to the Guide to Federal Records in the National Archives of the United States (Washington, D.C.: NARA, 1995).

Inventory of the Records of the United States Geological Survey, Record Group 57, in the National Archives, part of USGS Circular 1179 (2000, CD-ROM): Records and History of the United States Geological Survey, contains information on USGS and related records accessioned by NARA through 1997 and held at NARA-II. Appendices in this inventory list field records held at NARA-II and by the USGS Field Records Library at Denver.

National Archives and Records Administration

8601 Adelphi Road

College Park, MD 20740-6001

Telephone: 301-713-6800 (General Reference Information)

Telephone: 1-866-272-6272 (Toll Free)

E-mail: inquire@nara.gov

URL: http://www.archives.gov/index.html

The Smithsonian Institution Archives

Arts and Industries Building, Room 2135

900 Jefferson Drive, S.W.

Washington, D.C. 20560

Telephone: 202-357-1420

E-mail: OSIAREF@OSIA.SI.EDU

Rocky Mountain Mapping Center

USGS National Mapping Division

Box 25046, MS 506, Federal Center

Denver, CO 80225-0046

Telephone: 303-202-4394

Mid-Continent Mapping Center

USGS National Mapping Division

MS 309

1400 Independence Road

Rolla, MO 65401

Telephone: 573-308-3663

A wide variety of maps are available from the USGS national mapping program in both paper and digital form. Check our list of earthquake and fault maps first. If you don't find what you are looking for there, the following links also have map information:

This Dynamic Planet: World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics
Dibblee Geological Foundation Maps - for some of California, with roads and towns
California Geological Survey
Other State Agencies

You can also contact your state geological survey and/or your county geologist. The Association of American State Geologists has compiled a directory of state geological organizations, which provides addresses, telephone numbers, and staff.

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

Probably. Visit our Geologic Information pages or we will take a look for you.

A: For flood insurance maps, contact the Federal Emergency Management Agency (FEMA), Flood Map Division.

Telephone: 1-800-358-9616
FAX: 1-800-333-1363
URL: http://store.msc.fema.gov

For prints of historical flood-prone area maps on microfilm, contact:

U.S. Geological Survey
Earth Science Information Center
507 National Center
Reston, VA 20192

Telephone: 1-888-ASK-USGS (1-888-275-8747) or 703-648-5953
FAX: 703-648-5548
TDD: 703-648-4119
E-mail: ask@usgs.gov

• 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

 

A landslide hazard map indicates the possibility of landslides occurring throughout a given area. A hazard map may be as simple as a map that uses the locations of old landslides to indicate potential instability, or as complex as a quantitative map incorporating probabilities based on variables such as rainfall thresholds, slope angle, soil type, and levels of earthquake shaking. An ideal landslide hazard map shows not only the chances that a landslide may form at a particular place, but also the chance that it may travel downslope a given distance.

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

This type of maps ranks slope stability of an area into categories that range from stable to unstable. Susceptibility maps show where landslides may form. Many susceptibility maps use a color scheme that relates warm colors (red, orange, and yellow) to unstable and marginally unstable areas and cool colors (blue and green) to stable areas.