It's not something I've ever really thought about in detail, but if anyone ever asked me what shape (generally) a medieval town would be when drawn on a map, I would have said either rectangular or circular. Those are the general shapes we see in books or games or even movies. We've also probably all heard some version of history that explains how towns grew up around castles, manor houses, cross roads, etc. Circles and rectangles therefore make sense.
I'm doing (more) research for my RK story set in Wales, however, and I've noticed something really interesting (at least to me):
Welsh villages tended to have vaguely triangular sprawls.
Or at least that's the way they appear to me on the old town plans I've been able to find. It has me wondering why, and if it may have something to do with the mountainous region in which the story takes place. If you're building in a valley between a couple of mountains, maybe triangular is the shape that makes the most sense.
Whatever the reason, though, I find it neat and thought I'd share. Especially since I don't believe I've ever seen such a thing in a work of fiction.