怎样让Google地图显示指定的城市？

<script src="http://maps.google.com/maps?file=api&v=2&sensor=false&key=ABQIAAAA9Ot9Dal8oVohqNGTUB61oRQLjaRHydcRGDb-HBpcbU38szWFQBR-wymCIqIGN6F1_4YQvg-O9H3ntg" type="text/javascript"></script>

    <script type="text/javascript">



    var map = null;

    var geocoder = null;



    function initialize() {

      if (GBrowserIsCompatible()) {

        map = new GMap2(document.getElementById("map_canvas"));

        map.setCenter(new GLatLng(39.917, 116.397), 13);/*这里我改成(121.4838, 31.2517), 3也不行*/

        geocoder = new GClientGeocoder();

      }

    }



    function showAddress(address) {

      if (geocoder) {

        geocoder.getLatLng(

          address,

          function(point) {

            if (!point) {

              alert("不能解析: " + address);

            } else {

              map.setCenter(point, 13);

              var marker = new GMarker(point);

              map.addOverlay(marker);

              marker.openInfoWindowHtml(address);

            }

          }

        );

      }

    }

    </script>



 <body  onload="initialize()" onunload="GUnload()">

    〖地理位置〗

    <div id="map_canvas" style="width: 500px; height: 300px"></div>