Topographic Maps

Topographic Maps Contour lines connect all points with the same elevation, and give a great picture of the lay of the land. The resulting map is called a Topographic Map. Sometimes you have to figure out the contour interval. Remember that the ocean is at sea level and elevation is how far you are above sea level.

Close lines = Steep Slope There are several important rules to remember when reading a topographic map: Close lines = Steep Slope Contour lines bend upstream when crossing a river Since contour lines must remain at the same elevation, they must bend when they cross riverbeds. A riverbed drops downward, so the contour line must bend uphill to stay at the same elevation. The highlighted lines show that the direction of the Mill River must be northeast.

Highest possible elevation of a hill The last line indicated on the map is 220 meters. The next line would be 240 meters (remember that the contour interval is 20 meters). Since there is no 240 meter line, the hill cannot be higher than 239 meters!

•Depressions are shown by small marks pointing inward off the contour line The arrow is pointing to a depression, or hole. The contour line with the marks, or hatchers, has the same elevation as the line before it. In this case the hatchered line has a value of 140 meters, and the depression must be less than 140 meters.

Profiles A profile is a picture of what the landscape would look like from the side. It is a cross section of the landscape. Given this topographic map, which of the four choices below accurately depicts the correct profile between points X and Y?

Drawing a profile from a topographic map:

Draw two points on opposite sides of the map, and connect them with a line segment. Label the endpoints A and B. Place a piece of scrap paper over your map and align it to segment AB as shown below. Mark the endpoints on the scrap paper. Then, make a tick mark on the scrap paper at every contour line, as shown. Write the appropriate elevation next to each tick mark.

Create a graph like this one: Place the scrap paper on the 900 meter line of this graph so that the A endpoint is lined up with the y-axis , as shown below. Plot any 900 m points on the line.

Repeat for the other elevations marked on the scrap paper Repeat for the other elevations marked on the scrap paper. Make sure that for each elevation, endpoint A is always lined up with the y-axis. The last step is to connect the dots on the graph with a smooth line as shown below. Now you have a profile of the landscape! http://www.explorelearning.com/index.cfm?method=cResource.dspExpGuide&ResourceID=493