Gradient (Slope)
Topographic maps are not just used for determining elevation, they can also be used to help visualize topography. The key is to study the pattern of the contour lines, not just the elevation they represent. One of the most basic topographic observation that can be made is the gradient (or slope) of the ground surface. High (or steep) gradients occur in areas where there is a large change in elevation over a short distance. Low (or gentle) gradients occur where there is little change in elevation over he same distance. Gradients are obviously relative. What would be considered steep in some areas (like Ohio) might be considered gentle in another (like Montana). however we can still compare gradients between different parts of a map.
On a topographic map the amount of elevation change is related to the number of contour lines. Using the same contour interval the more contour lines over the same distance indicates a steeper slope. As a result areas of a map where the contour lines are close together indicate steeper slopes. Areas with widely spaced contour lines are gentle slopes. The map below examples of areas with steep and gentle gradient. Note the difference in contour line spacing between the two areas.
Compare the slope of the west side of Spruce Knob with the slope of the east side. Which side is steeper?.....
.....The east side. Notice the spacing between the contour lines. Contour lines on the east side of Spruce Knob are closer together than the contour lines on the west side indicating steeper slopes.
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Last Updated: 03/11/2008