Geographers, cartographers and military surveyors use protractors to determine the angular direction between two points located on a two-dimensional map. While a traditional semicircular protractor measuring 0-180° angles can be used, a circular or square protractor would be more accurate for this task, as they both use 360° and are divided into four sections (the four cardinal directions), thus providing better precision for both compass quadrants and azimuth bearings. The protractor measures the compass quadrant bearing between 0-90°, and azimuth angle from 0-360°. A military protractor can also be used, though it is less user-friendly, and is designed primarily to measure azimuth and back azimuth angles.
- Skill level:
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Things you need
- Circular or square protractor
- Pencil or ruler
Place the map on a flat surface. Identify points A and B, with A being the starting point from which you are measuring and B the destination whose angular direction you need to determine.
Place the vertex (or centre) of the protractor on point A, making sure that it is oriented parallel to the map's north-south gridline. Draw a line from point A to B (or use a ruler if you don't want to mark the map).
Determine the compass bearing by identifying the angle where the line intersects the protractor. Decide if it's closer to the north or south baseline on the protractor. Then determine whether it's closer to the due east or west lines. This will be its quadrant. Write down the N or S direction first, then the compass bearing angle (between 0-90°, measured from the N or S) line, followed by E or W. (For example, if the line intersects at 73° in the southeast quadrant, it is written as S 73° E.)
Ascertain the azimuth bearing by measuring clockwise from the north baseline of the protractor down to where your line intersects it. This the azimuth angle. In the example listed in Step 3, the azimuth angle would be 107°.
Tips and warnings
- Avoid using a semicircular protractor if possible. Since it only measures between 0-180°, it becomes more complicated to measure compass bearing and azimuth angles in the lower SW and SE quadrants, and requires reorienting the protractor and performing additional calculations. A circular or square protractor can be purchased for about the same price.
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