Click for Coverage
  • JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler
X

The USGS Map and Why You Need One

Posted in How To on March 19, 2003
Share this

When you're in the middle of nowhere and need to know exactly where you are, few things come more in handy than a U. S. Geological Survey (USGS) map. Sure, a Global Positioning System (GPS) can tell you exactly where you are anywhere on the planet, but that information isn't worth squat if you forgot to punch in where you started from or you don't have a map that can show you where your coordinates are in relation to where you want to be. When you're lost and low on gas, that information can literally be a lifesaver. A set of USGS maps for the area you plan to 'wheel should be a part of your trail arsenal.

The U.S. Department of the Interior offers several types of USGS maps for sale to the public, but the ones that apply most to four-wheeling enthusiasts are topographic maps, or topos for short. These maps are available in several scales. The most useful maps are the 7.5-minute versions because they supply the greatest amount of detail--1:24,000-scale (1 inch equals 2,000 feet). Each USGS topo map divides the country into squares called quadrangles, and a 7.5-minute map shows an area that spans 7.5 minutes of longitude and 7.5 minutes of latitude (between 49 and 64 square miles depending on the latitude). It takes about 57,000 7.5-minute maps to cover all of the United States and its territories, so the practical approach for using 7.5-minute maps is to purchase only the maps that cover the area you plan to 'wheel in.

Topos show the topography of an area by means of contour lines along with cities, towns, bodies of water, rivers, roads, and boundaries. Whenever possible, the names of these points as well as mountains, mountain ranges, valleys, forests, and plateaus are indicated. This information indicates what the terrain of the area looks like, where the towns are located, and where water can be found, all of which are important to know during an off-road foray. But once you know where all this stuff is, you'll need to be able to navigate your way there, which is where longitude and latitude come in.

Topo maps have longitude and latitude designations in the border around the map, and sometimes lines indicating longitude and latitude are drawn right on the map. If you have the coordinates (longitude and latitude) of a known point (also called a waypoint) on the map and know the coordinates of your location, you can figure out the best way to travel from one point to another by using the topographical information. Finding the exact coordinates of a point on the map is easy with the help of a waypoint finder, but of course the trick is to pinpoint your exact location (this is where a GPS is very handy).

If you would like more information on how to navigate the old-fashioned way (without a GPS), information on USGS maps and the maps themselves are available though several sources. Your nearest USGS Earth Science Information Center (ESIC) has detailed booklets that offer additional information on USGS maps as well as indexes, catalogs, and order forms to help you select the maps you want. Many will also have local maps in stock. If there isn't an ESIC in your area, some merchants may sell local maps that cover popular local recreational areas. We've found them at some sporting goods stores, specialty map stores, and even at a couple of off-road shops. There may even be a class offered at your local community college. Also, check your local library for USGS maps. If all else fails, maps can be purchased by mail directly from the Department of the Interior, although it takes three-five weeks for delivery.

Once you have a set of USGS maps in hand and become familiar with how to read them, you'll wonder how you ever lived without them.

Among other things, USGS topographical maps have brown contour lines that indicate the features and elevation of terrain. It may take some practice to match the terrain indicated on the map with the terrain in front of you, but as a general rule remember that the more closely spaced the brown contour lines are, the more drastic the elevation change. The contour lines have regular intervals that indicate elevation in feet. Among other things, USGS topographical maps have brown contour lines that indicate the features and elevation of terrain. It may take some practice to match the terrain indicated on the map with the terrain in front of you, but as a general rule remember that the more closely spaced the brown contour lines are, the more drastic the elevation change. The contour lines have regular intervals that indicate elevation in feet.
Here's an example of the navigational information found on the margins around a USGS map. The latitude coordinates are always found in the vertical margins, and longitude is always indicated in the horizontal margins. North is always at the top of the map. Minutes and seconds for both longitude and latitude are notated with tick marks just like the abbreviations for feet and inches; one tick mark indicates minutes, and two indicate seconds. This particular map has dotted lines and crosses that indicate longitude and latitude instead of the thin red lines found on some. Many people recommend adding solid lines over the dotted lines if the user plans to navigate with the map. Here's an example of the navigational information found on the margins around a USGS map. The latitude coordinates are always found in the vertical margins, and longitude is always indicated in the horizontal margins. North is always at the top of the map. Minutes and seconds for both longitude and latitude are notated with tick marks just like the abbreviations for feet and inches; one tick mark indicates minutes, and two indicate seconds. This particular map has dotted lines and crosses that indicate longitude and latitude instead of the thin red lines found on some. Many people recommend adding solid lines over the dotted lines if the user plans to navigate with the map.
There is more useful information to be found at the bottom of the map in the margins. The one drawback to some USGS maps, especially those that cover the remote areas where trails are often found, is that they aren't updated very often. Although the basic topography doesn't change, it's common that roads are added or deleted over the years, and many boundaries that affect land use may have changed. The name of the specific map (all maps are named after a prominent feature or city in the area they cover), the original date of publication, and the last time it was updated are at the bottom of the map. As you can see, this map was last updated in 1957! Always check with local forest service or BLM officials if you're not sure about the land's status for motorized use. There is more useful information to be found at the bottom of the map in the margins. The one drawback to some USGS maps, especially those that cover the remote areas where trails are often found, is that they aren't updated very often. Although the basic topography doesn't change, it's common that roads are added or deleted over the years, and many boundaries that affect land use may have changed. The name of the specific map (all maps are named after a prominent feature or city in the area they cover), the original date of publication, and the last time it was updated are at the bottom of the map. As you can see, this map was last updated in 1957! Always check with local forest service or BLM officials if you're not sure about the land's status for motorized use.

Sources

USGS Information Services
Denver, CO 80225

Connect With Us

Newsletter Sign Up

Subscribe to the Magazine

Browse Articles By Vehicle

See Results