function kjmapType() {
      kjmapType.prototype.tileSize = new google.maps.Size(256,256);
      kjmapType.prototype.minZoom = 8;
      kjmapType.prototype.maxZoom = 16;
      kjmapType.prototype.name = '今昔マップ　首都圏編 明治期';
      kjmapType.prototype.alt = '今昔マップ　首都圏編 明治期';
      kjmapType.prototype.getTile = function( tileXY, zoom, ownerDocument ) {
         var tileImage = ownerDocument.createElement('img');
         var ymax = 1 << zoom;
         var y = ymax - tileXY.y - 1;
         var dataSetFolder = "tokyo50"; //データセットのフォルダ指定
         var ageFolder = "00";   //データセット内の時期別フォルダ指定
         var src = "http://ktgis.net/kjmapw/kjtilemap/"
                  + dataSetFolder + "/"
                  + ageFolder + "/"
                  + zoom + "/"
                  + tileXY.x + "/"
                  + y
                  + ".png";
         tileImage.setAttribute("src", src);
         tileImage.style.width = this.tileSize.width + "px";
         tileImage.style.height = this.tileSize.height + "px";
         return tileImage;
      };
   }
   
   var map;
   kjmapTypeObj = new kjmapType();
   function init_google_map() {
      var mapOptions = {
         zoom: 15,
         center: new google.maps.LatLng( 35.678257,139.715512 ),
         streetViewControl: true,
         mapTypeId: google.maps.MapTypeId.ROADMAP,
         mapTypeControlOptions: {
            mapTypeIds: [ google.maps.MapTypeId.ROADMAP, 'kjmap' ],
            style: google.maps.MapTypeControlStyle.HORIZONTAL_BAR
         }
      };
      var mapDiv = document.getElementById('map_canvas');
      map = new google.maps.Map( mapDiv, mapOptions );
      map.mapTypes.set('kjmap', kjmapTypeObj);
      });
   }