< Profile

A map view looks at the surface of the earth from overhead. Contour maps use the contour lines to represent the third dimension of elevation. In a previous lesson we examined geologic maps. We also looked at geologic cross sections that cut through the earth and showed the rocks beneath the surface. The top line on the cross section represented the surface of the earth. We can apply this same alteration of perspective to contour maps. From the information provided by the contour map, we can produce a cut across this surface into the earth and, thus, show a side view like a silhouette or skyline. This illustration is called a TOPOGRAPHIC PROFILE.

A topographic profile is a diagram that shows the change of elevation of the land surface along a given line. As indicated above, it represents graphically the skyline viewed from a distance. The VERTICAL scale is the scale used to plot the elevation. It is usually larger than the horizontal or map scale, EXAGERATED, in order to emphasize the difference in the relief. The MAXIMUM RELIEF is the difference in elevation between the highest and lowest points.

Following are the steps for drawing a topographic profile.

1. Lay the edge of a strip of paper along the line between the starting and ending points for the profile.
2. Mark on the edge of the strip the EXACT places where each CONTOUR, STREAM, and HILLTOP crosses this line.
3. Label these marks with the elevation and correct identification.
4. Mark any important other features such as bottoms of depressions or landmarks to be included.
5. If a graph is not provided, construct the horizontal line for your profile of the SAME LENGTH as your profile (unless a different horizontal scale is to be used for the profile.) Generally, the same horizontal scale is used. Prepare the VERTICAL SCALE by lightly drawing lines parallel to your horizontal base line on the proper scale for each of the elevations to be represented. Label these lines with the correct elevations starting one or two intervals below the lowest elevation that will be plotted (lowest elevation on the profile). Thus, the side represents a kind of graphic scale.
6. Place the edge of the strip of paper with the labeled contour lines at the bottom of the profile base line and project each contour and feature to the horizontal line of the same elevation. Put a small dot at the intersection of these two lines.
7. Connect all of the points with a smooth line being careful to show all hilltops at the proper height and all valleys and depressions at their correct approximate values.


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