private int getZLevel(final GeoPrimitive item) {
        if (item != null && item.getZLevel() >= 0) {
            return item.getZLevel() + 20;
        }
        return defaultZLevel + 20;
    }
mimics {@link #removeItem(MarkerInterface)} but w/o calling 'populate'
main/src/main/java/cgeo/geocaching/unifiedmap/geoitemlayer/MapsforgeVtmGeoItemLayer.java