What is the definition of magnetic variation?

Magnetic variation, also known as magnetic declination, is defined as the angular difference between true north and magnetic north. True north refers to the direction along the Earth's surface towards the geographic North Pole, while magnetic north points to the location of the North Magnetic Pole, which is the point on the Earth's surface where magnetic field lines point vertically downwards.

This difference is important for navigation, especially for pilots and mariners who rely on compasses. For effective navigation, pilots must understand and compensate for this variation, especially when converting between headings (true and magnetic) and when using charts that depict true north. As the magnetic North Pole shifts over time, magnetic variation can also change, which is why it is essential for pilots to use the latest aeronautical charts or navigational data that provide current variation values for their area of operation.

In contrast, the other options describe differences that are not related to magnetic variation. True north and geographic north are essentially the same, and differences between magnetic north and grid north pertain to the grid system used for navigation rather than the magnetic compass. Additionally, the elevation difference mentioned in the last option does not relate to directional navigation at all.