Where is the declination diagram of a map located and what does it illustrate?

The declination diagram of a map is located in the lower margin and illustrates the angular relationship between true north, magnetic north, and grid north. This is essential for navigation, as it helps users understand how to accurately orient themselves and the map in relation to the Earth's magnetic field and its grid system. By providing this information, the declination diagram enables individuals to make necessary adjustments when using a compass or when navigating in areas where the map's coordinate system is in use.

In the context of navigation, understanding this angular relationship is crucial for accurate directional movement, especially in areas where magnetic declination can vary significantly. The placement in the lower margin ensures it is readily accessible as users examine the map, facilitating quick learning for effective navigation.

The other options, while they may reference elements found on a map, do not accurately describe the specific characteristics or location of the declination diagram.