@Override
    protected void onSaveInstanceState(@NonNull final Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putBundle(STATE_ROUTETRACKUTILS, routeTrackUtils.getState());
    }
to be called by map fragments' observers for zoom level change
main/src/main/java/cgeo/geocaching/unifiedmap/UnifiedMapActivity.java