A compass needle gives you magnetic north. A map lets you use that direction to estimate where you are and decide which way to go. The two are useful when a phone loses power, has poor reception or shows a position that does not fit the terrain.
This guide covers two tasks: estimating your position from landmarks and setting a bearing for a leg of your route. Practise both on familiar ground before relying on them in poor visibility.
Get to know a baseplate compass
A baseplate compass has a clear plate, a rotating housing marked in degrees and a magnetic needle inside it. Look at your own compass so you can find the parts mentioned below.
- Magnetic needle. The north end, often red or marked N, points to magnetic north when the compass is held level. Move away from objects that can deflect it, such as a phone, magnet, steel railing or some equipment. Check that the reading stays steady when you move away.
- Rotating housing. The degree scale runs around the capsule. Inside are parallel orienting lines and a north arrow.
- Direction-of-travel arrow. This arrow on the baseplate points towards the landmark or destination you are sighting.
- Index line. Read the number on the rotating scale at this fixed mark on the baseplate.
Identify the north end of the needle and the north end of the orienting arrow. They are different from the direction-of-travel arrow.
Orient the map to the ground
Check the map’s north information. True north, grid north and magnetic north can differ. The following steps use a plain compass with no built-in declination correction in use, and a map marked with local magnetic north lines. You can find those lines for Japan in GSI Maps. Print or mark them in advance.
Here is how to orient a map with those lines.
- Lay the baseplate edge parallel to a marked magnetic north line, with the direction-of-travel arrow pointing towards its north end.
- Rotate the housing until N, or 0°, is at the index line.
- Keep the compass in place and turn the map and compass together until the north end of the needle aligns with the north arrow in the housing.
The magnetic north lines now point towards magnetic north on the ground. A top edge or grid line may point towards a different north. The angle between true and magnetic north is magnetic declination, and it varies by location and date. Use the map information and the Geospatial Information Authority of Japan (GSI) to check the local value. If you use an adjustable compass with a correction already set, follow its manual and use the appropriate map north reference. Applying both corrections would shift the bearing twice.
Estimate your position from landmark bearings
If terrain alone leaves several possibilities, try resection. Identify at least two visible landmarks that you can also locate precisely on the map. Peaks, saddles or mapped structures can work if you are sure which one you see.
The steps
- Orient the map and choose a distinct landmark A that you can identify on it.
- Hold the compass level and point the direction-of-travel arrow towards A. Rotate the housing until the north end of the needle lines up with the north arrow in the housing. The index now shows the magnetic bearing to A.
- Without changing the housing setting, place one long edge through A on the map. Rotate the entire compass around A until the lines in the housing are parallel to the map’s magnetic north lines and the housing’s north arrow points towards magnetic north on the map.
- Draw along the edge from A back towards your approximate location, opposite the direction-of-travel arrow.
- Repeat with a second landmark B in a different direction.
- The crossing of the two lines gives an estimate of your position.
Check that the crossing fits the terrain you see, your approximate elevation and your last known position. A third bearing can help check the result. The lines can form a small area rather than meeting at a point. A large mismatch calls for another check of the landmarks, north reference and readings.
Common errors
- The landmark is missing from the map or you have identified the wrong one. Check its shape and surroundings.
- The housing turns while you move the compass to the map. Hold the baseplate steady and recheck the index.
- The bearing lines meet at a shallow angle. Look for landmarks in well-separated directions, ideally producing a crossing near a right angle.
Set and follow a bearing
Once you know your position, use the map to choose a safe next leg. A bearing tells you a direction. Check that the line does not cross a cliff, river, closure or other obstacle, and use established routes.
Take the bearing from the map
- Place the long edge along the line from your position to the next waypoint, with the direction-of-travel arrow pointing towards the waypoint.
- Turn the housing so its orienting lines are parallel to the map’s magnetic north lines and the housing’s north arrow points towards magnetic north on the map.
- Read the magnetic bearing at the index line and leave the housing set to that bearing.
Follow the bearing on the ground
- Lift the compass off the map and hold it level in front of you with the travel arrow pointing away from you.
- Turn your body until the north end of the needle aligns with the north arrow in the housing. Keep the housing setting.
- Identify a landmark along the direction-of-travel arrow that you can safely reach along your planned route. Check the terrain before moving.
In good visibility, choose a feature such as a rock or tree on the bearing and walk to it by the safe route. Check the bearing and your progress again from there.
In limited visibility, counting paces can help estimate distance on safe, familiar terrain. Measure your average distance over a known stretch beforehand. Slope, footing and pack weight change your stride. Treat the count as an estimate and avoid moving into unfamiliar terrain if you cannot confirm where you are.
When the compass and your sense of direction disagree
Stop in a safe place and check what could explain the difference.
- Magnetic interference. Move away from steel and electronics and repeat the reading.
- A map or compass error. Start again and verify which north reference you are using, the index setting and the direction of the arrows.
- A mistaken impression of the terrain. Compare several landmarks with the map, starting from your last confirmed point.
Fatigue and poor visibility can affect your sense of direction. Use the compass, map and terrain together. If the position remains uncertain, return along your known route to the last confirmed point when it is safe to do so. If you cannot move safely, stop and seek help as conditions allow.
A distinct feature such as a mapped junction on a ridge can help confirm your location. Learning to read those features makes each compass reading easier to interpret.
Before your next hike
Try map orientation and bearings on familiar paths in a park or on a low hill. Practise with a current 1:25,000 map or a suitable equivalent, and check the magnetic north information before leaving. You can ask the Nordwand community about practising together when you have a connection.
References
- Geospatial Information Authority of Japan: GSI Maps and topographic map guidance
- Geospatial Information Authority of Japan: magnetic declination and magnetic north
- National Police Agency and prefectural police: mountain incident statistics and safety guidance