Knowing the grade of a route can provide a more comfortable and timely trek.
Grade lines describe the change in elevation, rise or fall, over a given distance on topographic maps. These changes in elevations correlate to the steepness of the terrain. Grade lines can be given as a percentage or as an angle with the greater angle or percentage corresponding to a steeper slope. A topographic map is a useful tool in calculating the grade as it shows the elevation through the use of brown lines called contour lines. Contour lines connect adjacent points of the same elevation so that all points on a given contour line share the same elevation.
Instructions
1. Draw a line on the topographic map along the path for which the grade is to be calculated.
2. Find the elevation for the contour lines along the grade line. Contour lines appear as brown lines on the map and appear in three varieties. Dark brown index contour lines typically have their elevation value labeled on the line. Light brown intermediate contour lines appear at equidistant intervals between index contour lines. The distance between intermediate contour lines is given in the contour interval on the bottom map margin. Supplementary contour lines are dashed light-brown lines that appear at half the value of an intermediate contour line.
3. Determine the lowest and highest elevation values for a continuous slope along the grade line. A continuous slope constantly increases or decreases along the given grade line.
4. Subtract the lowest elevation value from the highest elevation value to find the amount of elevation change between these two points.
5. Measure the horizontal distance between the two elevation points on the grade line.
6. Divide the vertical change in elevation by the measured horizontal distance then multiply by 100 to produce the grade line as a percent value (vertical distance/horizontal distance x 100 = % slope).
7. Calculate the angle of the grade line by dividing the vertical change in elevation by the horizontal distance to yield the tangent of the slope angle. Using the calculator, compute the arc tangent (inverse tangent) to determine the slope angle.
Tags: grade line, contour lines, horizontal distance, change elevation, elevation value, intermediate contour