Reading Topographic Maps
On a topographic map, hills are represented by a series of closed circles. For a hill the elevation of each contour line increases as you move towards the center of the circle.
Maximum Possible Elevation
The highest point on any hill, is inside the inner most circle. To figure out what the Maximum Possible elevation is, we need to follow a simple procedure:
- Find the highest contour line
- Figure out what the next line up would be
Maximum Possible Elevation = Next line -1
Let's Practice: Find the Maximum Possible elevation of point X on the map below.
Highest contour line = 1600m
Next line would be = 1700m
Max Possible Ele. of X = 1699m
Another recognizable landform on topographic map is a depression. A depression is sort of the opposite of a hill. It is a ditch, or gully, or pit, where the elevation decreases towards the center.
On a topographic map depressions look a lot like hills. They will appear as a series of closed circles one inside the other. However, to distinguish them from hills, depressions have hashmarks on all of the contour lines. This allows us to easily identify them as depressions.
Another important difference between hills and depressions is that the outermost contour line on a depressions always has the exact same value as the last normal contour line on the map.
Minimum Possible Elevation
The lowest point in a depression is inside the inner most circle. To find the Minimum Possible Elevation we need to follow another simple procedure:
- Find the lowest contour line
- Figure out what the next line down would be
Minimum Possible Elevation = Next line down + 1
Lowest contour line = 1260m
Next line down = 1240m
Min Possible Elevation = 1241m
Rivers are another common feature on topographic maps. Whenever a river crosses the landscape on a topographic map, the contour lines bend near the river creating a V shape on either side of the river. We can use the topographic maps to determine which way a river is flowing.
All water flows downhill, from areas of high elevation towards areas of lower elevation. The bending of the contour lines near the river always points uphill, which means RIVERS ALWAYS FLOW IN THE OPPOSITE DIRECTION FROM THE WAY THE CONTOUR LINES BEND.
In the example above, the contour lines have been highlighted to show how they bend. We can see that they make a V pointing to the Southwest. This means that the river flows in the opposite direction, Northeast.
Let's Practice: Find the direction of flow for the river shown below.
Contour lines bend pointing to the South.
River flows opposite = to the North.