by Jim Riesterer . . . . . . . . . . Edited by Scott Hughes, Dan Narsavage & Diana Boyack 

Topographic Maps TutorialIntroduction & MaterialsWhat is a Map?Using Topo MapsMap ScaleReference DatumMap ProjectionsDistortionsGrid SystemsGeographicUTMState PlanePublic Land SurveyVertical ScaleCreating ProfilesVertical ExaggerationCalculating SlopeUsing a CompassMagnetic DeclinationGet a BearingGo from A to BFind Self on a MapTopographic Maps Field ExercisesExercise 1Exercise 2Exercise 3Exercise 4GeoSTAC HomeField Exercisesgeostac@gmail.comApril 8, 2008 
Calculating a SlopeDetermining 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.
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. If the value you calculate is, for example, 20, then what this means is that for every 100 feet you cover in a horizontal direction, you will gain (or lose) 20 feet in elevation. To calculate the angle of the slope, divide the elevation change in feet by the distance of the line you drew (after converting it to feet). This is the tangent value for the angle of the slope. Apply an arctangent function to this value to obtain the angle of the slope (hit the ‘inv’ button and then the ‘tan’ button on most scientific calculators to get the slope angle). The angle you calculated is the angle between a horizontal plane and the surface of the hill. Using the example above, (click here or on image for larger picture) a hill with a 20% slope is equivalent to an 11° slope. Continue to ... Compass ... 