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May 2019 Issue
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How to combine map and compass

Photo: Matthew Cattin

The compass is an extremely useful accessory to the map. By Noel Bigwood

There are many situations in which direction of travel needs to be determined. You might be at a car park with multiple tracks leaving from it and be unsure which is the one you should take. There may be no signs, or they may not help – does Rimu Track go to Rimu Creek or to a stand of rimu? Or perhaps you want to find the bearing of a feature you intend to follow, for example, a track, river, ridge or a feature you can see in the distance.

There are two methods for determining a bearing with your compass.

1. Identify a bearing from a map

1. First locate on the map where you want to travel – e.g. track, river or ridge.

2. Place the compass on the map with one edge of the compass along the line you want to travel. Ensure the direction of travel arrow on the compass is facing the direction you wish to travel.

3. Rotate the dial until the red and black orienting lines in the base of the dial line up with the blue north-south grid lines on the map. Ensure the red end of the orienting lines face to the top of the map.

4. You have now set the compass for the grid bearing. You can now read the bearing as the number around the dial in line with the direction of travel arrow. The figure shows a bearing of 270° or west.

5. To face this bearing, find on the map the magnetic variation for the area. This is the difference between magnetic and grid bearings. In our example, the variation is 24°.

6. Hold the compass level in front of you with the direction of travel arrow away from you at 90° degrees to the line of your shoulders. Move your feet to rotate your body until the red magnetic needle points to 24° – the magnetic variation. You are now facing the direction of your bearing.

7. If you walk with the red magnetic needle pointing to the magnetic variation, you will be travelling in the direction of the bearing.

2. Identify a bearing of a feature from a map

When in the field, you may wish to find the bearing of a feature you intend to follow, for example, a track, river, ridge or a feature you can see in the distance.

1. Hold the compass as described in point 6 above and face the feature.

2. Turn the dial until the red magnetic needle points to the magnetic variation (24° in this example).

3. You have now set the compass for the bearing for the feature. As before, you can now read the bearing as the number around the dial in line with the direction of travel arrow.

4. You can put this on to the map with your current location on one edge of your compass. Without moving the dial, move the compass until the red and black orienting lines line up with the blue north-south grid lines on the map. Ensure the red end of the orienting lines face to the top of the map.

5. Your feature should be along the edge of the compass. It may be a little bit off depending on the line you have chosen because features like tracks and rivers are not dead straight. If it is completely off, consider if you have identified the feature correctly.

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