Why does the difference between true north and grid north occur?

The distinction between true north and grid north arises from the earth's geography and the layout of the map projection being used. When projecting the curved surface of the Earth onto a flat map, certain distortions occur, particularly in terms of grid lines and their orientation.

Grid lines are constructed based on a specific projection, which can lead to variations in angle and spacing, especially as one moves closer to the poles. At the equator, grid lines are typically more spread out, reflecting the Earth's curvature in a manner that allows for a more accurate representation in that area. However, as one approaches the poles, these grid lines converge, which means they get closer together. This convergence creates a difference in direction between true north—which refers to the direction of the North Pole—and grid north, which is defined by the orientation of the grid lines on the map.

In this case, the correct understanding lies in recognizing how the integrity of grid lines changes with latitude, ultimately leading to the difference between grid north and true north as geographical distortions occur, particularly near the poles.