Reading Steepness from Contour Lines

Equation: the ground slope between two contour lines is slope = rise / run = contour interval / horizontal distance between the lines. Values: the rise is the contour interval, 5 ft, from the note on the plan; every pair of neighbouring lines differs by 5 ft (135, 130, 125 …). The run is the horizontal spacing between lines measured on the plan. Step 1: the rise is the same everywhere on the map, 5 ft per line. Step 2: in Area 1 the lines are close together, so the run is short. In Area 2 they are far apart, so the run is long. Step 3: the same rise over a shorter run gives a larger slope. For example, lines 20 ft apart give 5/20 = 25%, while lines 100 ft apart give 5/100 = 5%. Area 1 is a steep slope. Widely spaced lines, as in Area 2, mean flatter ground. A closed depression would show closed loops, usually with hachure marks, and these lines are open. Contours alone do not indicate water.