Slope or Gradient
Slope can be expressed as the slope ratio or gradient, the angle of slope, or the percent of
slope. The slope ratio is a fraction in which the vertical distance is the numerator and the
horizontal distance is the denominator. The angle of slope in degrees is the angular
difference the inclined surface makes with the horizontal plane. The tangent of the slope
angle is determinedly dividing the vertical distance by the horizontal distance between
the highest and lowest elevations of the inclined surface. The actual angle is found by
using trigonometric tables. The percent of slope is the number of meters of elevation per
100 meters of horizontal distance. Slope information that is available to the analyst in
degrees or in ratio values may be converted to percent of slope by using a nomogram.
FM 5-33 US Army Field Manual, Terrain Analysis, p. 1-1