These are things published by Avalon Game Company, and I quite like the idea (I haven't actually read any of them, so I'm uncertain how it works in practice; the company's quality seems a bit... variable). Each describes a small area of the game world - one hex in this case - in detail.
Supplements covering large regions are cool, but it would be also cool to see small, probably electronic, supplements covering small regions in detail, whether this be urban or not. Given enough of them, they could be combined into a printed book.
I doubt Terry has the time for doing something like this (unlike he completely gives up on that silly idea called "sleep") but it could be the sort of thing that fans and GM's could do - for one thing, at least some probably have areas like this already described in detail.
