@Override
 protected void refreshNotes() {
   noteOverlay.clear();
   for (Note note : sessionManager.getNotes()) {
     noteOverlay.add(note);
   }
 }
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    noteOverlay.setContext(this);

    setContentView(R.layout.heat_map);

    mapView.getOverlays().add(routeOverlay);
    mapView.getOverlays().add(traceOverlay);

    if (!sessionManager.isSessionSaved()) {
      mapView.getOverlays().add(locationOverlay);
    }
  }