public synchronized TileLayer setBaseMap(final TileSource tileSource) {
        removeBaseMap();

        final VectorTileLayer l = new OsmTileLayer(mMap);
        l.setTileSource(tileSource);
        addLayerToGroup(l, LayerHelper.ZINDEX_BASEMAP);
        baseMap = l;
        return baseMap;
    }
call this instead of VTM.setBaseMap so that we can keep track of baseMap set by tile provider
main/src/main/java/cgeo/geocaching/unifiedmap/mapsforgevtm/MapsforgeVtmFragment.java