distance between 2 lat/long coord

distance.js

/* This function calculates distance with the Haversine formula, t
   his formula assumes that our Earth is spherical, 
   but it isn’t since it’s more like a big orange fruit also compresses at poles. 
   I’ve read that this function has an error about + o – 3 meters (it depends), 
   but it’s a small error for many purposes. 
   http://snipplr.com/view/25479/
*/

function distance(lat1,lon1,lat2,lon2) {
	var R = 6371; // km (change this constant to get miles)
	var dLat = (lat2-lat1) * Math.PI / 180;
	var dLon = (lon2-lon1) * Math.PI / 180;
	var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
		Math.cos(lat1 * Math.PI / 180 ) * Math.cos(lat2 * Math.PI / 180 ) *
		Math.sin(dLon/2) * Math.sin(dLon/2);
	var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
	var d = R * c;
	if (d>1) return Math.round(d)+"km";
	else if (d<=1) return Math.round(d*1000)+"m";
	return d;
}