Determining the Difference in Elevation
Contour lines are the continuous brown lines found on topographic maps. They provide a reference for elevation. Every 5th contour line is dark brown. These lines are called "Index Contours", and often have a number associated with them that indicates the elevation they represent. The distance between contour lines is called the "Contour Interval". All USGS 7.5 minute quadrangle topographic maps will have the words "Contour Interval 20 Feet" either in the map legend or in the bottom frame. The number 20 indicates their is an elevation change of 20ft between contour lines. This interval may vary if they are not USGS 7.5 minute quadrangle maps, so please be sure to check the interval in the legend at the bottom of the map.
To determine the difference in elevation between two points, determine the elevation at each point and then calculate the difference. Record your answer in feet. In the example below, point A is at 1220 ft. and point B is at 1800 ft. The difference between 1800 ft. and 1220 ft. = 580 ft.
