If you ever thought about building a hierarchical navigation tree menu for administrative geographic regions, you should really have a look at GeoTree (via GeoNames Blog) Will save you a lot of time. It would be cool if you also had the polygons for each of the nodes in the tree, basically a complete, non-overlapping hierarchical polygon structure that you could use to select all objects that lie within a specific region that you pick from the tree. This would actually be quite a nice case of geographic brushing again. Mouse-over France in the map and highlight France on the navigation tree at the same time – and vice versa. How about a non-administrative tree? A tree which is built up of natural areas? It would probably be a lot harder to draw sharp boundaries, since mountains, and natural habitats have rather fuzzy boundaries. But this gets us into the „where do mountains begin“ question and it means we’re drifting off. I guess we wouldn’t mind overlapping natural habitats and just select all objects in boundary regions more than once then.