@Override
    public void setZoom(final int zoomLevel) {
        final MapPosition pos = mMap.getMapPosition();
        pos.setZoomLevel(zoomLevel);
        mMap.setMapPosition(pos);
    }
call this instead of VTM.layers().add so that we can keep track of layers added by the tile provider
main/src/main/java/cgeo/geocaching/unifiedmap/mapsforgevtm/MapsforgeVtmFragment.java