Magnetic declination is the angle between the geographic north direction (polar north) and the magnetic north direction (needle north). The difference is due to the fact that the horizontal component of the Earth's magnetic field is not parallel to the geographical north direction.
The magnetic declination is different at different points on the earth's surface. It also changes slowly over time as the Earth's magnetic field changes. The deviation and its rate of change are usually marked on maps and nautical charts in the declension rose.
