Retrieving coordinates of two addresses using Google Maps and calculating distance

So here’s a quick couple snippets of code that will allow you to retrieve the coordinates of two locations using Google Maps API — no API key necessary.

This first function will return the coordinates of specific address (I find pretty much anything works, whether it’s a full address with street number, or just a postal code, or simply a city name) as an array of coordinates:

function getCoordinates($address) {

  $url = "http://maps.google.com/maps/geo?q=" . urlencode($address)

         . "&output=json";

  $result = file_get_contents($url);

  $result = json_decode($result, 1);

  if (isset($result['Placemark'])) {

    list($lat, $long) = $result['Placemark'][0]['Point']['coordinates'];

  } else {

    $lat = $long = false;

  }

  return array($lat, $long);

}

and the following function will accept the lat/long coordinates of two separate points and return their distance (not road/traveling distance, but straight-shot distance) in KM:

function calculateDistance($lat1, $long1, $lat2, $long2) {

  $R = 6371; // earth's mean radius in km

  $dLat = deg2rad($lat2-$lat1);

  $dLon = deg2rad($long2-$long1);

  $lat1 = deg2rad($lat1);

  $lat2 = deg2rad($lat2);



  $a = sin($dLat/2) * sin($dLat/2) +

      cos($lat1) * cos($lat2) *

      sin($dLon/2) * sin($dLon/2);

  $c = 2 * atan2(sqrt($a), sqrt(1-$a));

  $d = $R * $c;



  // return distance in KM

  return $d;

}

Now it certainly may be worthwhile to cache coordinates for a given location, depending on your usage, because retrieving the coordinates from Google for a large quantity of addresses at once can take some time.