A compass error caused by the difference in the locations of the earth’s geographic north pole and its magnetic north pole. All navigation charts and maps are drawn with reference to the geographic north pole, and all magnetic compasses point to the magnetic north pole. These two locations are not the same, and they are only in alignment along the agonic line.

At any particular location on the surface of the earth, the variation error is the same for all headings. Variation is called declination in land navigation.