What is the angular difference between grid and geodetic north referred to in map projections?

The angular difference between grid north and geodetic north is known as the convergence angle. This angle is crucial in understanding how the grid system on a map, which aligns with a specific projection, relates to the true geographic orientation provided by geodetic north. The convergence angle varies depending on the location on the Earth's surface and the specific map projection being used, influencing how accurately you can navigate or represent distances on a map.

On the other hand, the angle of incidence refers to the angle at which incoming rays strike a surface, which is not directly related to the concepts of grid or geodetic north. The deviation angle is typically used to describe the angle between a compass direction and true north, but it isn't applicable in this context where the focus is on map projections. The azimuth angle refers to the angle measured from a specific reference point, usually true north, to a target point, again not addressing the specific difference between grid and geodetic north. Thus, convergence angle is the correct term for this particular relationship in map projections.