Distance Between Points

distance.js

// Manual: Haversine Formula: shortest route over a sphere
function distance(latlng1, latlng2) {
  var R = 6371, // Radius of the earth, in km. Need miles? change to 3961
      dLat = (latlng2.lat - latlng1.lat) * (Math.PI/180),
      dLon = (latlng2.lng - latlng1.lng) * (Math.PI/180),
      a = Math.sin(dLat/2)*Math.sin(dLat/2) +
          Math.cos(latlng1.lat * (Math.PI/180)) *
          Math.cos(latlng.lat * (Math.PI/180)) *
          Math.sin(dLon/2) * Math.sin(dLon/2),
      c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)),
      d = R * c;
  
  return d;
}

// Google Maps v3 with Geometry Library
// @see https://developers.google.com/maps/documentation/javascript/geometry
google.maps.geometry.spherical.computeDistanceBetween( latLngA, latLngB );