function initialize() {
var map = new GMap2(document.getElementById("map_canvas"));
map.addControl(new GSmallMapControl());
map.addControl(new GMapTypeControl());
map.setCenter(new GLatLng(51.524018,0.104542), 13);


// Creates a marker whose info window displays the letter corresponding
// to the given index.
function createMarker(point, index) {
  // Create a lettered icon for this point using our icon class
  var letteredIcon = new GIcon();
  letteredIcon.image = "http://www.protocoluk.com/images/protocolDownArrow.png";
  letteredIcon.iconSize = new GSize(30, 30);
  letteredIcon.iconAnchor = new GPoint(10, 20);   
  letteredIcon.infoWindowAnchor = new GPoint(13, 2);
  // Set up our GMarkerOptions object
  markerOptions = { icon:letteredIcon };
  var marker = new GMarker(point, markerOptions);

  GEvent.addListener(marker, "click", function() {
    marker.openInfoWindowHtml("<span style=\"font-size: 9px \">Protocol Office Limited<br />2-3 Bankside Park,<br />28 Thames Road,<br />Barking,<br />Essex,<br />IG11 0HZ<br />United Kingdom.</span>");
  });
  return marker;
}

// Add 10 markers to the map at random locations
var bounds = map.getBounds();
var southWest = bounds.getSouthWest();
var northEast = bounds.getNorthEast();
var lngSpan = northEast.lng() - southWest.lng();
var latSpan = northEast.lat() - southWest.lat();

  var point = new GLatLng(51.524018,0.104542);
  map.addOverlay(createMarker(point, 1));

}