Magnetic declination is an important concept for accurate navigation. A compass will always point along the lines of magnetic force (which converge on what are called the magnetic poles). The angle between the direction of force and the direction of the geographic north pole is called the declination. If a compass at your location is pointing to the right of true north, declination is positive or east, and if it points to the left of true north, declination is negative or west. As one moves across the surface of the globe, lines of constant magnetic declination are called isogonic lines.

As the earth’s magnetic field varies over time, the positions of the north and south magnetic poles gradually change. The magnetic declination at a given location also changes over time.