@NonNull
    public static synchronized MapSource getMapSource() {
        if (mapSource != null) {
            return mapSource;
        }
        final String mapSourceId = getString(R.string.pref_mapsource, null);
        mapSource = MapProviderFactory.getMapSource(mapSourceId);
        if (mapSource == null || !mapSource.isAvailable()) {
            mapSource = MapProviderFactory.getAnyMapSource();
        }
        return mapSource;
    }
@return zoom used for the map of a single cache
main/src/main/java/cgeo/geocaching/settings/Settings.java