Topo or topographic maps are specialized maps that show us a 3 dimensional world in a 2 dimensional format.
Topographic maps do that via “Contour Lines” that indicate elevation. Generally shown in brown, these lines divide the map into areas of equal elevation. All areas on a given line are “on the level” that is to say that the contour line connects areas of the same elevation; thus if you were to walk along a contour line you would do no climbing nor descending on your trip. You’ll only gain or lose elevation if you travel to another contour line.
The spacing of the Contour Lines is indicative of the rate of change (how steep an area is). Widely spaced lines tell you that the slope is relatively gentle, while closely spaced lines show a steeper area.
To illustrate this relationship let’s look at an example of a topographic map.
In this example you’ll see that contour lines are connected and that the relative spacing of those lines indicates the incline of the area. In the top most sketch at point A you see that the contour lines are closely spaced. In the side view at the bottom of the drawing point B shows the slope described in A.
Conversely, if an area has widely spaced contour lines the slope is gentle. As seen on the left side of the drawing.
Now that you know what a contour line is, it’s time to discuss Contour Intervals.
A Contour Interval is the amount of vertical distance described by each contour line. The value is generally given in the map legend. If the contour interval given is 10 meters then each line shows a 10 meter change in elevation. Maps with a smaller contour interval show a more detailed picture of the area in question.
What common terrain features look like on a topo map
Closely spaced Contour lines that run along a stream indicate a steep canyon.
The V end of a Contour Line always points upstream.
Look closely at this map of East Fork State Park in Ohio. You’ll see that the trail (indicated by the dashed line) runs along a drainage that flows into a larger body of water.
The blue arrows point upstream along a main drainage into the lake.
The red arrows point upstream along several secondary drainages.
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