Tile clusters are a combination of tiles you have visited, that are connected to each other.
But thats not enough!
To be accepted as a part of a cluster, all the sides of the tiles have to be also visited tiles.
So the next tiles to north, east south and west have to be visited tiles also.
In the white/grey color indicates a clustered tile (a tile which all the connecting tiles from the sides are also visited).
Yellow/golden color indicates a tile which you have visited, but is not part of a cluster.
A tile can be at the same time a part of a megatile and a cluster. Or it can be a part of a megatile, but not cluster.
