InitializeMap with Overlay

var overlay;
USGSOverlay.prototype = new google.maps.OverlayView();
var info = new google.maps.InfoWindow();

function initialize() {
  var mapOptions = {
    zoom: 0,
disableDefaultUI: true,
streetViewControl: false,
navigationControl: false,
zoomControl: false,
scaleControl: false,
scrollwheel: false,
disableDoubleClickZoom: true,
    center: new google.maps.LatLng(28.70, -127.50),
    mapTypeId: google.maps.MapTypeId.ROADMAP

  };

  var map = new google.maps.Map(document.getElementById('map-canvas'), mapOptions);

var marker = new google.maps.Marker({
    position: map.getCenter(),
    map: map
  });

  var swBound = new google.maps.LatLng(62.281819, -150.287132);
  var neBound = new google.maps.LatLng(62.400471, -150.005608);
  var bounds = new google.maps.LatLngBounds(swBound, neBound);
    var allowedBounds = new google.maps.LatLngBounds(
                  new google.maps.LatLng(28.70, -127.50),
                  new google.maps.LatLng(48.85, -55.90)
                );

                var boundLimits = {
                    maxLat : allowedBounds.getNorthEast().lat(),
                    maxLng : allowedBounds.getNorthEast().lng(),
                    minLat : allowedBounds.getSouthWest().lat(),
                    minLng : allowedBounds.getSouthWest().lng()
                };

                var lastValidCenter = map.getCenter();
                var newLat, newLng;
                google.maps.event.addListener(map, 'center_changed', function() {
                    center = map.getCenter();
                    if (allowedBounds.contains(center)) {

                        lastValidCenter = map.getCenter();
                        return;
                    }
                    newLat = lastValidCenter.lat();
                    newLng = lastValidCenter.lng();
                    if(center.lng() > boundLimits.minLng && center.lng() < boundLimits.maxLng){
                        newLng = center.lng();
                    }
                    if(center.lat() > boundLimits.minLat && center.lat() < boundLimits.maxLat){
                        newLat = center.lat();
                    }
                    map.panTo(new google.maps.LatLng(newLat, newLng));

                });

  var srcImage = 'assets/pics/floorImage.jpg';

  overlay = new USGSOverlay(bounds, srcImage, map);
}

function loadScript() {
      var script = document.createElement('script');
      script.type = 'text/javascript';
      script.src = 'https://maps.googleapis.com/maps/api/js?v=3.exp&' +
          'callback=initialize';
      document.body.appendChild(script);
    }

window.onload = loadScript;
function USGSOverlay(bounds, image, map) {

      this.bounds_ = bounds;
      this.image_ = image;
      this.map_ = map;

      this.div_ = null;

      this.setMap(map);
    }

    USGSOverlay.prototype.onAdd = function() {

      var div = document.createElement('div');
      div.style.borderStyle = '0';
      div.style.borderWidth = '100%';
      div.style.position = 'b';

      var img = document.createElement('img');
      img.src = this.image_;
      img.style.width = '800px';
      img.style.height = '500px';
      img.style.position = 'absolute';
      div.appendChild(img);

      this.div_ = div;

      var panes = this.getPanes();
      panes.overlayLayer.appendChild(div);
    };

    USGSOverlay.prototype.draw = function() {

      var overlayProjection = this.getProjection();

      var sw = overlayProjection.fromLatLngToDivPixel(this.bounds_.getSouthWest());
      var ne = overlayProjection.fromLatLngToDivPixel(this.bounds_.getNorthEast());

      var div = this.div_;
      div.style.left = sw.x + '10';
      div.style.top = ne.y + '10';
      div.style.width = (ne.x - sw.x) + '';
      div.style.height = (sw.y - ne.y) + '50';
    };

    USGSOverlay.prototype.onRemove = function() {
      this.div_.parentNode.removeChild(this.div_);
      this.div_ = null;
    };


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