Tell me more ×  What is the delta between two lat/lon pairs
called? Delta degrees? Arcs?  Is it some quantity of distance
but what is its unit of measurement?  And related: Can we use
pythagoras to calculate this distance?  eg. d = (0, 3) and (4,
0) = 5?  share|improve this question add comment  2 Answers  up
vote 6 down vote accepted  You can't use the simple Pythagorean
theorem as that one's for planes whereas the distances you are
talking about now are on a curve. For that, you'll have to use
spherical trigonometry. From Wikipedia:  Let enter image
description here be the geographical latitude and longitude of
two points (a base "standpoint" and the destination
"forepoint"), respectively, and enter image description here
their absolute differences; then enter image description here,
the central angle between them, is given by the spherical law of
cosines:  enter image description here  The distance d, i.e. the
arc length, for a sphere of radius r and enter image description
here  given in radians, is then