An angular difference between true north and either magnetic or grid north is known as what?

The angular difference between true north and magnetic or grid north is known as declination. Declination is crucial for navigation and map reading, as it helps individuals understand the variation between the direction of true north, which is based on the Earth's rotational axis, and magnetic north, which is determined by the Earth's magnetic field. This difference can impact navigation accuracy, especially when using a compass, as compasses point toward magnetic north rather than true north.

Understanding declination allows navigators and map users to adjust their bearings accordingly, ensuring they stay accurate in their travel direction. It is particularly important in areas where the magnetic declination is significant, which can vary based on geographic location and even change over time.