var map;function initialize() {  var mapOptions = {    zoom: 15,    center: new google.maps.LatLng(37.78313383212, -122.4039494991302)  };  map = new google.maps.Map(document.getElementById('map-canvas'),      mapOptions);
  var bounds = {    17: [[20969, 20970], [50657, 50658]],    18: [[41939, 41940], [101315, 101317]],    19: [[83878, 83881], [202631, 202634]],    20: [[167757, 167763], [405263, 405269]]  };
  var imageMapType = new google.maps.ImageMapType({    getTileUrl: function(coord, zoom) {      if (zoom < 17 || zoom > 20 ||          bounds[zoom][0][0] > coord.x || coord.x > bounds[zoom][0][1] ||          bounds[zoom][1][0] > coord.y || coord.y > bounds[zoom][1][1]) {        return null;      }
      return ['http://www.gstatic.com/io2010maps/tiles/5/L2_',          zoom, '_', coord.x, '_', coord.y, '.png'].join('');    },    tileSize: new google.maps.Size(256, 256)  });
  map.overlayMapTypes.push(imageMapType);
}
google.maps.event.addDomListener(window, 'load', initialize);