A bearing is just an angle, but three rules are attached so that everybody reads it the same way. Measure from north. Turn clockwise. Write it with three figures.
The three rules
| Rule | Why it exists |
|---|---|
| Always measure from NORTH | North is the one direction everyone can find. Measuring from anything else would depend on where you happen to be standing |
| Always turn CLOCKWISE | If some turned one way and some the other, a bearing of 60 would mean two different directions |
| Always write THREE figures | So 60 degrees is written 060 and can never be misread over a radio |
North is 000, east is 090, south is 180 and west is 270. A bearing can name any direction at all, including one halfway between north east and east, which ordinary words cannot do.
Students put the protractor on the road, the river or the edge of the page instead of on the north line. Before you measure anything, draw the north arrow at the point you are measuring from, and make sure the zero of your protractor sits on it.
Back bearings
If you know the bearing of B from A, the bearing of A from B is the back bearing. Add 180 if the original is less than 180, and subtract 180 if it is 180 or more.
The north lines at A and at B are parallel, because north is the same direction everywhere. The line joining A to B cuts both, so the angle at A and the angle at B are co-interior angles and must add to 180. That is the whole reason.
Scale drawing
A scale drawing has every length reduced by the same factor. A scale of 1 cm to 5 m means a wall drawn 7 cm long is really 35 m long. A scale written 1 : 500 means 1 cm on the drawing is 500 cm on the ground.
A scale drawing and the real thing are similar figures. Every length is multiplied by the scale factor and every angle is unchanged. That is why a bearing measured on a map is the true bearing on the ground, and no calculation is needed.
Most wrong answers here come from mixing centimetres and metres. Write the scale down as a sentence in words first: one centimetre stands for five metres. If the numbers look far too large or too small at the end, you have slipped a factor of a hundred somewhere.
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