By Jim Riesterer.......... Edited by Scott Hughes, Dan Narsavage & Diana Boyack Topographic Maps Tutorial Topographic Maps Field Exercises geostac@gmail.com April 8, 2008 Calculating a Slope Determining the average slope of a hill using a topographic map is fairly simple. Slope can be given in two different ways, a percent gradient or an angle of the slope. The initial steps to calculating slope either way are the same. • Decide on an area for which you want to calculate the slope (note, it should be an area where the slope direction does not change; do not cross the top of a hill or the bottom of a valley). • Decide on an area for which you want to calculate the slope (note, it should be an area where the slope direction does not change; do not cross the top of a hill or the bottom of a valley). • Once you have decided on an area of interest, draw a straight line perpendicular to the contours on the slope.
For the most accuracy, start and end your line on, rather than between, contours on the map. • Measure the length of the line you drew and, using the scale of the map, convert that distance to feet. Droid Razr Maxx Root Wifi Tether. (insert image with the line drawn on it, conversion calculation) • Determine the total elevation change along the line you drew (subtract the elevation of the lowest contour used from the elevation of the highest contour used). You do not need to do any conversions on this measurement, as it is a real-world elevation change. To calculate a percent slope, simply divide the elevation change in feet by the distance of the line you drew (after converting it to feet). Multiply the resulting number by 100 to get a percentage value equal to the percent slope of the hill.