[Codein]

Possibley so you can expand it in any direction as you please? As opposed to simply expanding right and top.

Say like you had a town on the left of the map, and you wanted some more grass/forest/what ever there, then on a traditional graph, you'd have to move everything right by how much space you want on the left, but with Rick's graph, you can expand it in any direction without having to move anything.