Bearing and back bearing: a trek to the village
Trek from a camp to a village on a bearing read from a map, then find the bearing that brings you back. Change the bearing, the length on the map and the scale, and find the back bearing and the real distance.
Core concept
The back bearing points the opposite way: it is the bearing + 180° if the bearing is less than 180°, and the bearing − 180° otherwise; on a scale drawing, real distance = map distance × scale
Topic: Bearing and scale drawing
A bearing is a direction measured clockwise from north, written with three figures: east is 090°, south is 180°. If a village is on a bearing of 060° from your camp, then to come back you face the opposite way. Turning round adds half a turn, 180°: the back bearing is 060° + 180° = 240°. If the bearing is 180° or more, adding 180° would pass 360°, so take 180° away instead: the back bearing of 240° is 060°. Trekkers also use a scale drawing: the real distance is the distance on the map × the scale, so 5 cm at 1 cm = 2 km is 10 km.
What you will learn
- Find the back bearing from a bearing.
- Explain why the bearing and the back bearing differ by 180°.
- Use a scale to find a real distance from a map.
Before you start
- Know three-figure bearings measured clockwise from north.
Materials
- A trekking map or a map of your district
Equipment
- A protractor, a ruler and a compass
Procedure
- Record the village 5 cm away on the map at 1 cm = 2 km, bearing 060°.
- Change the bearing to 240° and record.
- Record a bearing of 000°, then 180°.
- Change the scale to 1 cm = 5 km and record.
How this simulation is simplified
- The ground is flat, north is the same direction at the camp and at the village, and north is at the top of the map.