I see what you mean. I did think about a 'County' grouping - e.g. East of England is a bit wide. But Counties change, and you could miss out ona site just over the border.

I don't think there's an ideal solution to the grouping question. That's where the map browser comes into it's own, I think. I'd like to see more 'non-site' detail on there though, such as major roads / towns etc. as an aid to navigation maybe only at higher zoom levels.