// please change this as needed
 
  MAP_URL    = "map.html"

  MAP_WIDTH  = 770
  MAP_HEIGHT = 411



 function map_open() {
  var w,
      x = Math.floor( (screen.width  - MAP_WIDTH)  / 2),
      y = Math.floor( (screen.height - MAP_HEIGHT) / 2);
  
   w = window.open
        (
          MAP_URL, 

          "_blank", 

         (
          "width=" + MAP_WIDTH + ",height=" + MAP_HEIGHT + "," +
           "location=no,menubar=no,resizable=no,toolbar=no,scrollbars=no," +
           "screenX=" + x + ",screenY=" + y + ",left=" + x + ",top=" + y
         )
        );
 }