var centreLat=20;
    var centreLon= -18.514286;
    var initialZoom=2
    var map; //the GMap2 itself


    function customGetTileURL(a,b) {
      //converts tile x,y into keyhole string

      var c=Math.pow(2,b);

        var d=a.x;
        var e=a.y;
        var f="t";
        for(var g=0;g<b;g++){
            c=c/2;
            if(e<c){
                if(d<c){f+="q"}
                else{f+="r";d-=c}
            }
            else{
                if(d<c){f+="t";e-=c}
                else{f+="s";d-=c;e-=c}
            }
        }
        return "/images/40_V55_1550_Venice_recto-tiles/"+f+".jpg"
    }

    function init() {
      if (GBrowserIsCompatible()) {
        //resizeMapDiv();
        var copyright = new GCopyright(1,
                              new GLatLngBounds(new GLatLng(-90, -180),
                                                new GLatLng(90, 180)),
                              0,
                              "<a href=\"http://www.library.yale.edu/maps\">Yale Maps</a>");
        var copyrightCollection = new GCopyrightCollection("Imagery Property of ");
        copyrightCollection.addCopyright(copyright);

        //create a custom picture layer
        var pic_tileLayers = [ new GTileLayer(copyrightCollection , 0, 17)];
        pic_tileLayers[0].getTileUrl = customGetTileURL;
        pic_tileLayers[0].isPng = function() { return false; };
        pic_tileLayers[0].getOpacity = function() { return 1.0; };
        var pic_customMap = new GMapType(pic_tileLayers, new GMercatorProjection(5), "Pic",
            {maxResolution:4, minResolution:0, errorMessage:"Data not available"});


        //Now create the custom map. Would normally be G_NORMAL_MAP,G_SATELLITE_MAP,G_HYBRID_MAP
        map = new GMap2(document.getElementById("map"),{mapTypes:[pic_customMap]});
        map.addControl(new GSmallMapControl());
        map.addControl(new GMapTypeControl());
		map.addControl(new GOverviewMapControl(new GSize(250,150)));
        map.enableDoubleClickZoom();
		map.enableContinuousZoom();
		map.enableScrollWheelZoom();
        map.setCenter(new GLatLng(centreLat, centreLon), initialZoom, pic_customMap);

/////////////////////////////////////////////////////////////////////////////////////
//Add any markers here e.g.
//      map.addOverlay(new GMarker(new GLatLng(x,y)));
/////////////////////////////////////////////////////////////////////////////////////

      }
    }
window.onload = init;
window.onunload = GUnload;