Marker cluster key displayed below (index value in parenthesis). Zoom in / out of the map to see the recalculation of the cluster sizes.

1. Cluster level 1 (index = 1)
2. Cluster level 2 (index = 2)
3. Cluster level 3 (index = 3)
4. Cluster level 4 (index = 4)
5. Cluster level 5 (index = 5)