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.
