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How to read a topographic plan

A topographic plan depicts a landscape through a series of contour lines. Each line indicates a constant elevation—a measured height above sea level or other reference point. Several keys help in reading a topographic plan:

• The direction of slope is perpendicular to the contours. A meandering drop of rainwater moves perpendicular to the contour lines, from higher to lower elevation.
• Where contour lines are closely spaced, the terrain is steep; where farther apart, flatter.
• If a nearby lake were to flood to a given elevation, the outline of the lake would match a contour line.
• If discerning a ridge (or crown) from a gully (ditch) is difficult, place yourself on the plan at the edge of the ridge or gully, and imagine yourself walking straight across it. At each step, verify the elevation on the plan to determine if you are going up or down.

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