A hierarchical quad-tree to encode the land/sea mask.
Each node in the tree can have up to 4 sub-trees, which can be either full trees or empty nodes.
If a node has no sub-trees, it represents a sea tile.
If a node has sub-trees, it represents a mixed tile.
If a node has no sub-trees and is not a leaf node, it represents a land tile.
A hierarchical quad-tree to encode the land/sea mask. Each node in the tree can have up to 4 sub-trees, which can be either full trees or empty nodes. If a node has no sub-trees, it represents a sea tile. If a node has sub-trees, it represents a mixed tile. If a node has no sub-trees and is not a leaf node, it represents a land tile.