function initialize() {

  if (navigator.geolocation)
  {
      var position = navigator.geolocation.getCurrentPosition();
      yourLat = position.coords.latitude;
      yourLng = position.coords.longitude;
      var myLatlng = new google.maps.LatLng(yourLat, yourLng);
      var mapOptions = {
        zoom: 4,
        center: myLatlng
      }
      var map = new google.maps.Map(document.getElementById('your-map-canvas'), mapOptions);

      var marker = new google.maps.Marker({
          position: myLatlng,
          map: map,
          title: 'Hello World!'
      });
  }
}

google.maps.event.addDomListener(window, 'load', initialize);