public MapDataManager(MapView mMapView, ResourceProxy rProxy) {
   mapView = mMapView;
   mContext = mMapView.getContext();
   mResourceProxy = rProxy;
   initializeOverlays(mContext);
   mapView.setMapListener(this);
   loadMapTask = new LoadMapDataTask();
   loadMapTask.execute(); // load graph and nodes to display
 }