Which of the following describes a declination diagram?

A declination diagram is specifically designed to illustrate the angular relationships between the three types of north: grid north, magnetic north, and true north. This is crucial for navigation and map reading, as it helps users understand the discrepancies between the various forms of northing in their navigational activities.

Understanding the declination is essential because magnetic north is not the same as true north; they can vary based on location due to the magnetic variations of the Earth. The declination diagram allows users to correct their compass readings by showing how far they deviate from true north. This information is vital for ensuring accurate navigation, especially in military operations where precision is crucial.

The other choices do not relate to the primary function of a declination diagram. Elevation changes on a map pertain to topographic features, military symbols concern map representation and communication, and a tool for measuring distances focuses on scale and measurement rather than directional relationships.