@NonNull
    public static synchronized AbstractTileProvider getTileProvider() {
        if (tileProvider != null) {
            return tileProvider;
        }
        final String tileProviderId = getString(R.string.pref_tileprovider, null);
        tileProvider = TileProviderFactory.getTileProvider(tileProviderId);
        if (tileProvider == null /* || !tileProvider.isAvailable() */) {
            tileProvider = TileProviderFactory.getAnyTileProvider();
        }
        return tileProvider;
    }
@return zoom used for the map of a single cache
main/src/main/java/cgeo/geocaching/settings/Settings.java