An exploration of the magnetic Earth · WMM2025
North is not a place.
A map gives you one direction. A needle gives you another. Between them is a small, moving angle that can take you off course.
Choose a place. Look at the two norths. Then walk with them for a while.
A compass does not tell you where north is. It tells you how the magnetic field behaves here.
01 · two answers
The needle is not looking for the North Pole.
A compass aligns with the direction of the local magnetic field. A map aligns with the Earth’s geographic axis. Both are correct. Each measures something different.
The angle between them is magnetic declination. A + sign means the needle falls east. A − sign means it falls west.
02 · the instrument
Where you stand changes the answer.
Choose a place and a year. The calculation below uses World Magnetic Model 2025, NOAA and the British Geological Survey’s navigation model.
at this place, in this year
03 · distance makes the angle visible
A small error has long legs.
If you treat a map bearing as a direct compass reading, the sideways drift grows with distance. Move the slider and see how much.
The calculation uses distance × sin(|declination|). It does not include terrain, missed steps, or nearby iron.
At 10 km, an angle of just five degrees means almost 872 m sideways.
04 · the Earth slowly changes the instrument
The map holds still. The field keeps moving.
The model is updated every five years because changes in the magnetic field accumulate. You will not feel it on a day hike. In a map used for years, it becomes part of the instrument.
The vertical scale adapts to the place so the small change remains visible.
05 · what a compass cannot see
North is an agreement, not a point.
When we say “north”, we compress three things into one word: the geographic axis, the local magnetic field, and the map’s convention. Orientation works when we know which one is doing the work.
how it was calculated
A simple model for an old question.
I used the public WMM2025 coefficients and the spherical synthesis formula supplied by NOAA. The result is the main-field declination at sea-level altitude for the selected coordinates. It is an orientation map, not a measurement from your phone in this exact minute.
Sources and limits
The model does not include rapid variation from geomagnetic storms or fine local crustal anomalies. For real navigation, check your instrument and the conditions on the ground.