Maps and compasses use north as a reference direction, but there are two important kinds of north. True north points toward the geographic North Pole, the fixed point where Earth’s rotation axis meets the surface. Magnetic north points toward the north magnetic pole, which is not in the same place.
Knowing the difference matters because even a small angle error can send a hiker, pilot, or surveyor far off course over distance.
The angle between true north and magnetic north is called magnetic declination. Declination can be east or west depending on where you are on Earth, and it changes slowly over time as Earth’s magnetic field shifts. Map users correct for declination when changing between a map bearing and a compass bearing.
A common rule is to add or subtract the local declination carefully, using the map’s declination diagram or a current local value.
Key Facts
- True north is the direction from your location to the geographic North Pole.
- Magnetic north is the direction a compass needle points, toward the magnetic north pole.
- Magnetic declination is the angle between true north and magnetic north.
- Declination east means magnetic north is east of true north at your location.
- Declination west means magnetic north is west of true north at your location.
- Corrected bearing = map bearing adjusted by local magnetic declination.
Vocabulary
- True north
- True north is the direction along Earth’s surface toward the geographic North Pole.
- Magnetic north
- Magnetic north is the direction a compass needle points because of Earth’s magnetic field.
- Magnetic declination
- Magnetic declination is the angle between true north and magnetic north at a specific location.
- Bearing
- A bearing is a direction measured in degrees clockwise from north.
- Compass rose
- A compass rose is a map symbol that shows directions such as north, east, south, and west.
Common Mistakes to Avoid
- Using compass north as if it were true north. This is wrong because a compass points to magnetic north, which may be several degrees away from true north.
- Ignoring whether declination is east or west. This is wrong because east and west declination require opposite corrections, so mixing them up increases the navigation error.
- Using old declination information from an outdated map. This is wrong because magnetic north moves over time, so the correct declination for an area can change.
- Measuring a map bearing but walking it directly with a compass without correction. This is wrong because map bearings usually reference true north, while the compass needle references magnetic north.
Practice Questions
- 1 A map bearing to a trail junction is 60 degrees true. The local magnetic declination is 10 degrees east. What compass bearing should you follow if your class rule is magnetic bearing = true bearing minus east declination?
- 2 A hiker follows a compass bearing that is 8 degrees off the correct direction. After walking 2 km, about how far sideways from the intended line is the hiker? Use sideways distance = distance × sin(angle), with sin(8 degrees) = 0.139.
- 3 A map shows true north straight up, but a compass needle points slightly to the right of the true north line. Explain what this tells you about the local magnetic declination and why a navigator must correct for it.