What adjustment is made to convert grid north to geodetic north?

To convert grid north to geodetic north, an adjustment known as the convergence angle is used. This angle accounts for the difference in direction between the grid north (the north direction based on the grid of a map projection) and geodetic north (the true north direction towards the North Pole).

When surveying or mapping, especially in areas where the Earth's curvature must be considered, the grid system can appear to deviate from true north due to the spherical shape of Earth. The convergence angle quantifies this deviation based on the specific location and orientation of the projection, and it allows surveyors to accurately relate grid-based measurements to true geographic coordinates.

By applying the convergence angle, surveyors can ensure their measurements align correctly with real-world directionality, which is vital for accuracy in various applications such as construction, land development, and navigation.