How to Represent a Steep Slope on Topographic Maps

Determine the representative fraction, or RF, that you will be using. The RF is always written with the map distance represented by 1 unit and the ground distance represented by the number of corresponding units. For example, an RF of 1:500 indicates that one unit on the map equals 500 units on the ground. The "map unit" and "ground unit" do not correspond to a specific unit of measure, but are decided upon by the map-maker. In this example, the "map unit" will be 1/4 inch and the "ground unit" will be 1 foot. Therefore, 1/4 inch:500 feet.

Record your RF on the map so anyone reading it knows your scale. In this example, write "1:500."

Measure the horizontal distance between the top of the steep slope and the bottom, using the tape measure, and record the number (for example, 1,500 feet).

Divide the number (1,500) by the denominator of your RF (in this example, 500), using the calculator. The resulting number corresponds to the numerator of your RF, which is always 1. So if your distance in step 2 is 1,500, your resulting number is 3 (1,500 divided by 500). This means that the distance will be denoted on your map with 3 units of the numerator, or 3 map units.

Measure the numerator distance on your paper, using the ruler, and mark it off. In this example, you would measure and mark off 3 units. In this case, that distance is 1/4 inch times 3, or 3/4 inch. This distance will represent the slope from its top to its bottom.

Draw parallel lines between the points. The lines should run horizontally on the slope. For a very steep slope, draw the lines very close together. The steeper the slope, the closer the lines. There is no specific formula for the spacing of the lines. It is up to you, the mapmaker, to be certain that you remain consistent throughout the map. That is, two slopes of similar steepness should have similarly spaced lines.

Draw an arrow from the top to the bottom of the slope. Write the word "down" in the direction of the slope.