Convergence of the meridians
The angular drawing together of the geographic meridians in passing form the Equator to the poles. At the Equator, all meridians are mutually parallel; passing from the Equator, they converge until they meet at the poles, intersecting at angles that are equal to their difference in longitudes. The term ‘convergence of meridians’ is used to also designate the relative difference of direction of meridians at specific points on the meridians. Thus, for a geodetic line, the azimuth at one end differs from the azimuth at the other end by 180 degrees plus or minus the amount of the convergence of the meridians at the end points.