National 4-H Forestry Invitational

How to Determine the Length and Bearing
of a Line

Topographic maps are frequently used in forestry as a tool for inventory and management of natural resources.  It is important to be able to measure distances, locate property boundaries, and recognize natural and man-made features on these maps.

This web site will help you learn how to use a compass and ruler to determine the following:

  • The length of a line established between two points on a topographic map.

  • The bearing (line of travel) between the two points using a mirrored-type Azimuth compass.

  • Correct the bearing for declination.


How to Determine the Length of a Line on a Topographic Map

For the topographic map contest, you will be given a 7.5 minute series topographic map with a line drawn on it between two points on the map as shown in the Photo 1 below.

Lay a ruler down on the map parallel to the line (see Photo 2 on the next page).  Position the zero-end of the ruler at Point A and measure the length of the line in inches from Point A to Point B.

Photo 1