How to Read a Bearing Compass for Surveying

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Reading a compass allows you to determine the bearing, or direction, location and how to get to a specific destination on a topographic map—a map which describes the shape of the land. The compass itself consists of a magnetic needle, regulated by a magnetic force, with a red tip that floats on a pivot point. The compass is surrounded by a rectangular, translucent base plate, which serves as a straight edge to help mark the bearing on the topographic map. The compass also consists of two arrows—direction of travel and an orienting arrow. There are also two important types of distinct markings on a compass—north label and 360 degree markings. The compass often includes the written four cardinal directions—north, south, east and west—or as degrees—the direction of north designated as 0/360 degrees, east as 90 degrees, south as 180 degrees and west as 270 degrees.

Mark both your present location and your destination on the topographic map with cross symbols (or any symbol you prefer to use).

Place the edge of the compass base plate in a way that it lies on both your present location marking and your destination marking. Your base plate should show you a straight path from point to point. Use the edge of the base plate to guide you as you draw a line, with your pencil, through your current location to your destination.

Move your compass over the line that you drew with your pencil. The center of the direction of travel arrow, or the compass needle, should be directly over the line drawn. The "north" or "0/360" marking on your compass should face directly up or the top of your map.

Differentiate between the true direction of north—in relation to a 360-degree circle, true north being 0 or 360 degrees—and north regulated by a magnetic force—in relation to the magnetic north pole from your current location. On a topographic map, the true direction of north is represented by a star symbol. The direction of the magnetic pole—which is directly proportional to the specific location—is represented by the letters "MN" for magnetic north. The direction of true north never changes. However magnetic north often changes.

Locate the numerical values, marked as degrees, of true north and magnetic north on your map and compass. The value of true north is written right beside the star symbol on the map. If magnetic north is to the right of true north, subtract the MN value from the true north value. If magnet north is to the left of true north, add the MN value to the true north value. The resulting calculation gives you a value known as the declination.

Use the declination value and track it on your compass to stay on path. This value should not change as you travel to your destination. This is how you know you are going in the right direction.

Things You'll Need

  • Compass
  • Topographic map
  • Pencil