js haversine

gistfile1.js

function calculateNearestCity(myGeo, cityGeo)
{
	//using the Haversine formula - http://en.wikipedia.org/wiki/Haversine_formula
	var deg2rad = Math.PI / 180,
		cos     = Math.cos,
		sin     = Math.sin,
		earth   = 6371; //radius of earth in km

	var derivedLat = (cityGeo.lat - myGeo.lat) * deg2rad,
		  derivedLon = (cityGeo.lon - myGeo.lon) * deg2rad;

	var haversine = sin(derivedLat / 2) * sin(derivedLat / 2) +
					cos(myGeo.lat * deg2rad) * cos(cityGeo.lat * deg2rad) *
					sin(derivedLon / 2) * sin(derivedLon / 2);

	return earth * (2 * Math.atan2(Math.sqrt(haversine), Math.sqrt(1-haversine)));
}