1078_1085_bi_c07_se 1/18/06 6:07 PM Page 1084 G Appendix T OPOGRAPHIC M APS How to Read a Topographic Map A map is a model that shows all or part of Earth’s surface on a flat surface such as a sheet of paper. There are many different types of maps. A topographic map is a map that shows the elevation of different points on Earth’s surface. It also shows many other features on Earth’s surface, including water, roads, and buildings. Direction on Maps Most maps are drawn so that north is at the top of the map and south is at the bottom. East is on the right side, and west is on the left. Most topographic maps have a small drawing called a compass rose that shows the different directions. The compass rose also shows magnetic north, which is the direction a compass points. An example of a compass rose is shown in the key of the topographic map in Figure 1. Contour Lines Look at the brown lines on the right-hand map in Figure 1. Each line connects points that are at the same elevation. For example, the brown contour line in the bottom right of the map is marked “1200.” This means that all points on this line are 1200 feet above sea level. In the United States, most topographic maps give contour intervals in feet rather than in meters. The thicker contour lines are called index contours. The difference in elevation between contour lines is called the contour interval. The contour interval for a given map is always the same. In Figure 1, the contour interval is 200 feet. The thin brown line just west of the 1200 contour is at 1400 feet. If you were to walk north from one contour line to the next, you would gain 200 feet in elevation. The closer together contour lines are, the steeper the terrain is. Near Dublin Lake, there are only a few contour lines, which indicates that the land is almost flat. Look at the area marked Summit, to the south of the lake. The contour lines there are very close together, which indicates a steep rock face. Horizontal Distance You have seen that vertical distances on maps are indicated using contour lines. Horizontal distances are indicated using a scale. Look at the scale on the map. Mt. Monadnock, N.H. Roads Trails Forest Exposed rock Figure 1 Contour interval Dublin Lake Contour interval 200 feet 0 0 1 2 mi 1 2 00 16 3 km Index contour 16 0 200 Wh ite Ar row Tr. 00 30 00 16 00 Campground State Park Hdqs. Parking Lot 00 12 Topography 1084 Appendix G Topographic Map 1200 Summit 3165 160 0 2000 20 00 16 00 12 00 Contour lines N Pum pe l ly T r ail Key 1078_1085_bi_c07_se 1/18/06 6:08 PM Page 1085 Depression Figure 2 Contour lines Index contour Hilltop V-shaped contours Commonly Used Map Symbols Contour line: elevation Contour line: depression School Primary highway Secondary highway Railroad tracks Airport River Stream Marsh or swamp Scale 0 1 Mile 0 Contour interval = 20 feet A scale indicates how much distance on a map is equivalent to a certain distance on Earth’s surface. Most topographic maps in the United States are at a scale of 1 : 24,000. This means that one inch on the map equals 24,000 inches on the ground (about 2000 feet). In the scale in Figure 1, the scale reads 1 inch = 1 mile. Topographic maps often also use a bar to show the scale of the map. To find a distance on a map, measure the distance using a ruler. Then, convert using the scale. For example, if the distance on the map is 4 inches, the distance on Earth’s surface would be 4 miles. Colors on Maps Different colors are used to indicate various features on topographic maps. As you have seen, brown lines are used to indicate elevation. Look near the Summit in Figure 1. Most of the area is white, which indicates an area with no trees. White areas can be open fields or bare rock. Much of the map is green, which indicates that the green areas are forested. The color blue indicates water. In Figure 1, this is Dublin Lake. Creeks, ponds, lakes, and oceans are also shown in blue on topographic maps. Red and black are used for artificial structures. For example, red and black are used to indicate roads. Trails are shown as dashed black lines. Densely populated areas are shown in either gray or red. 1 Kilometer Symbols on Topographic Maps Topographic maps use a wide variety of symbols that represent different features. For example, a contour line that forms a closed loop with dashes indicates a depression, or hollow, in the ground. The shape of the contour lines also can help to show ridges or valleys (see Figure 2). V-shaped contour lines pointing downhill indicate a ridgeline. V-shaped contour lines pointing uphill indicate a valley. Other common symbols used on topographic maps are shown on the map in Figure 2. Assessment Use the topographic maps shown to answer these questions. 1. From Dublin Lake, in what direction would you walk to get to the State Park Headquarters? 2. Is the area marked Summit flat or steep? How do you know? 3. What is the approximate elevation of the parking lot? 4. How far is it from Dublin Lake to the Summit? 5. Is the campground located in open or forested land? How do you know? 6. How might hikers make use of topographic maps? Topographic Maps 1085