What does a declination diagram illustrate?

A declination diagram illustrates the angular relationship between magnetic north, grid north, and true north. This is crucial for navigation because different types of north are used in various contexts and environments; true north refers to the geographic North Pole, while magnetic north is where a compass points, which can vary based on the local magnetic field. Grid north is the direction along the grid lines on a map, which are generally aligned with true north but may differ depending on the map projection being used.

Understanding this relationship is essential for accurate navigation and map reading, as it allows users to adjust their compass reading to align with the map's grid. This adjustment is necessary to ensure that navigators can accurately translate their compass direction into a corresponding direction on the map, preventing navigational errors that could arise from assuming that magnetic and true north are aligned. The other choices do not pertain to the specific purpose of a declination diagram.