Topographic maps show natural land features such as lakes, rivers, and mountain peaks as well as man-made features such as roads, railroad tracks, and canals. These maps also have contour lines that trace the outline of the terrain and show elevation. Contour lines suggest what the land looks like in three dimensions.
A contour interval is the distance between contour lines. For example, if a contour interval is 20 feet, every time you go up one contour line, the elevation increases by 20 feet. Conversely, every time you go down a contour line, the elevation decreases by 20 feet. When the contour lines are close together, the terrain is steep. When they’re spread apart, the terrain is closer to flat. Different maps have different contour intervals and the distance is usually noted in the map legend.
The most popular topographic maps for use within the U.S. are made by the United States Geological Survey (USGS). These maps cover different sizes of area; the smaller the area, the greater the detail. Topographic maps are often called topo maps. The topo maps that show the most detail are sometimes called quad sheets or 7.5 minute maps because they map just one quadrangle (geographer-speak for rectangular shaped piece of land) that covers 7.5 minutes of longitude and latitude A compass uses degrees to tell direction. North is 0 or 360 degrees, west is 90 degrees, south is 180 degrees, and east is 270 degrees. Most topographic maps show magnetic declination. Compass needles point to magnetic north, but most maps are oriented to true north. Because the earth’s magnetic field varies from place to place, magnetic north usually isn’t the same as true north; in the continental United States, the difference can be as much as 20 degrees. If you don’t account for the magnetic declination, you can get far off-course trying to navigate someplace with a compass. The declination tells you how many degrees you need to adjust your compass: If the declination is west, you subtract the degrees from 360 to get true north; if it’s east, you add the degrees.
Magnetic declination changes over time, and older USGS maps can have incorrect declination information printed on them. Using the wrong declination can cause all sorts of navigation problems, so check the current declination for your area at the following Web site: www.ngdc.noaa.gov/cgi-bin/seg/gmag/declination1.pl.
If your job or hobby takes you off the beaten path, you definitely need a topographic map. If you’re staying in your car, driving on paved roads, you probably don’t need a topographic map.
A contour interval is the distance between contour lines. For example, if a contour interval is 20 feet, every time you go up one contour line, the elevation increases by 20 feet. Conversely, every time you go down a contour line, the elevation decreases by 20 feet. When the contour lines are close together, the terrain is steep. When they’re spread apart, the terrain is closer to flat. Different maps have different contour intervals and the distance is usually noted in the map legend.
The most popular topographic maps for use within the U.S. are made by the United States Geological Survey (USGS). These maps cover different sizes of area; the smaller the area, the greater the detail. Topographic maps are often called topo maps. The topo maps that show the most detail are sometimes called quad sheets or 7.5 minute maps because they map just one quadrangle (geographer-speak for rectangular shaped piece of land) that covers 7.5 minutes of longitude and latitude A compass uses degrees to tell direction. North is 0 or 360 degrees, west is 90 degrees, south is 180 degrees, and east is 270 degrees. Most topographic maps show magnetic declination. Compass needles point to magnetic north, but most maps are oriented to true north. Because the earth’s magnetic field varies from place to place, magnetic north usually isn’t the same as true north; in the continental United States, the difference can be as much as 20 degrees. If you don’t account for the magnetic declination, you can get far off-course trying to navigate someplace with a compass. The declination tells you how many degrees you need to adjust your compass: If the declination is west, you subtract the degrees from 360 to get true north; if it’s east, you add the degrees.
Magnetic declination changes over time, and older USGS maps can have incorrect declination information printed on them. Using the wrong declination can cause all sorts of navigation problems, so check the current declination for your area at the following Web site: www.ngdc.noaa.gov/cgi-bin/seg/gmag/declination1.pl.
If your job or hobby takes you off the beaten path, you definitely need a topographic map. If you’re staying in your car, driving on paved roads, you probably don’t need a topographic map.
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