public synchronized void hide(final K key) {
        final Pair<GeoItem, Boolean> value = itemMap.get(key);
        if (value != null && value.second) {
            itemMap.put(key, new Pair<>(value.first, false));
            removeFromMap(key, value.first);
        }
    }
If an object for given key exists on the layer, it is made invisible
main/src/main/java/cgeo/geocaching/unifiedmap/geoitemlayer/GeoItemLayer.java