@Override
        public boolean equals(final Object obj) {
            if (!(obj instanceof MarkerSymbolCacheKey)) {
                return false;
            }
            final MarkerSymbolCacheKey other = (MarkerSymbolCacheKey) obj;
            return bitmap == other.bitmap // identity!
                && Objects.equals(xAnchor, other.xAnchor)
                && Objects.equals(yAnchor, other.yAnchor)
                && isFlat == other.isFlat;
        }
mimics {@link #removeItem(MarkerInterface)} but w/o calling 'populate'
main/src/main/java/cgeo/geocaching/unifiedmap/geoitemlayer/MapsforgeVtmGeoItemLayer.java