How to undersatnd topographic maps

1. Topography How to create and read a topographical map

2. BASICS Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you neither gain or lose elevation.

3. The shape of the island is shown by location shoreline on the map. Remember this shore line is a contour line. It separates areas that are above sea level from those that are below sea level. The shoreline itself is right at zero so we will call it the 0 ft. contour line (we could use m.,cm., in., or any other measurement for elevation).

4. But contour lines can have elevations other than sea level. We can picture this by pretending that we can change the depth of the ocean. The diagram below shows an island that is getting flooded as we raise the water level 10 ft above the original sea level.

5. By raising water levels to 20 ft and 30 ft above the original see level we can find the location of the 20ft and 30 ft contour lines. Notice our islands gets smaller and smaller

6. If we take each of the shorelines from the maps above and draw them on the same map we will get a topographic map (see map below). Taken all together the contour lines supply us with much information on the topography of the island. From the map (and the profile) we can see that this island has two "high" points

8. With practice we can picture topography by looking at the map even without the cross profile. That is the power of topographic maps

9. A common use for a topographic map is to determine the elevation at a specified locality. The map below is an enlargement of the map of the island from above. Each of the letters from A to E represent locations for which we wish to determine elevation. Use the map and determine (or estimate) the elevation of each of the 5 points. (Assume elevations are given in feet)

11. Unlike the simple topographic map used above, real topographic maps have many contour lines. It is not possible to label the elevation of each contour line. To make the map easier to read every fifth contour line vertically is an index contour. Index contours are shown by darker brown lines on the map. These are the contour lines that are usually labeled