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How do you estimate slope on a topographic map?

How do I find the slope on a topographic map?

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1. The slope is the change in altitude divided by the change in horizontal movement. The topo map will have curved lines indicating altitude. The altitude difference between two adjacent altitude lines is the change in altitude. Using the scale on the map, you can determine the horizontal distance between the altitude lines. Then just divide the change in altitude between adjacent lines and divide by the horizontal distance between the lines multiplied by the scaling factor. Be sure that you are using the same units. That is, if the altitude lines are in meters, be sure that you horizontal distance is also calculated in meters, not kilometers. Or if the change in altitude is in feet, the distance between the altitude lines must be converted to feet, not just left in miles.