The latitude of a point on a sphere is the elevation of the point from the plane of the equator. The latitude 
is related to the colatitude
(the polar angle in spherical coordinates)
by 
. More generally,
the latitude of a point on an ellipsoid is the angle
between a line perpendicular
to the surface of the ellipsoid at the given point
and the plane of the equator (Snyder 1987).
The equator therefore has latitude 
, and the north and south poles have latitude 
, respectively. Latitude is also called geographic
latitude or geodetic latitude in order to distinguish it from several subtly different
varieties of authalic latitudes.
The shortest distance between any two points on a sphere is the so-called great circle distance, which can be directly computed from the latitudes and longitudes of the two points.
