Important Note: The distance calculator on this page is provided for informational purposes only. The calculations are approximate in nature
This script calculates great-circle distances between the two points – that is, the shortest distance over the earth’s surface – using the ‘Haversine’ formula.
It assumes a spherical earth, ignoring ellipsoidal effects – which is accurate enough* for most purposes… – giving an ‘as-the-crow-flies’ distance between the two points (ignoring any hills!).
The Haversine formula ‘remains particularly well-conditioned for numerical computation even at small distances’ – unlike calculations based on the spherical law of cosines. (It was published by R W Sinnott in Sky and Telescope, 1984, though has been known about for much longer; the ‘half-versed-sine’ is (1-cosθ)/2, or sin²(θ/2) – don’t ask, I’m not a mathematician).
Since I tend to grab an area of the global or regional country maps I want, and then get the Boundary coords in MapCreator2, I then turn them into decimal and sort out the centre coords and then need to calc the Radius after that, which is where I found some serious 100% inaccuracies from the NOAA calculator especially in close. 29km NOAA > 74.18km Real.