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Geology Lab: Topographic Maps and Profiles

Terms in this set (28)

In order to create uniformity between various map publishers, contour lines must conform to certain guidelines:
1. A contour line connects points of equal elevation.
2. Contour lines separate all points of higher elevation from points of lower elevation.
3. A contour line never branches or splits.
4. Steep slopes are shown by closely spaced contours; gentle slopes are shown by widely spaced contours.
5. Contour lines never cross, except to show an overlapping or vertical cliff.
6. Hills are represented by a concentric series of closed contour lines.
7. A concentric series of closed contours with hachure marks represents a closed depression. Hachure marks point into the depression.
8. When contour lines cross stream valleys or dry stream channels, they form a "V" that points upstream.
9. Contour lines that occur on opposite sides of a valley (or hill) always occur in pairs. Single contour lines do not lay between maximum ridge and minimum valley contour lines.
10. To report a reversal of slope, you must repeat elevations. When crossing a hill, the last contour line crossed before reaching the top is the first one crossed when descending from the other side. The same is true when crossing a valley. In the example below, a person walking upslope would encounter the 340' contour line before the summit. Once they start their descent, the first contour line they encounter would be the 340' contour line. They were going upslope and now they are going downslope - a reversal of slope - so they will be repeating their elevation.
11. Topographic maps published by the USGS are contoured in feet or meters, usually referenced to sea level.