[Pierre-Marie Baty]

My system isn't a quadtree, it's a hashtable. The only difference with a "normal" hashtable is that the buckets in this hashtable are organized spatially along 2 axises, x and y (which I refer as "parallels" and "meridians" of the world).

Since these buckets are relatively small, they contain each a limited number of walkfaces, hence the cost of the search for neighbours remains low.

It's not the most elegant solution, but it's the simplest and the most effective in regard to its complication IMO.