Last August, I posted on codes and building types. As I mentioned, there are two main ways of doing codes. One is a matrix-based approach of clean categories, and the other is type-based. The type-based one tends to branch. A townhouse is a kind of house: a branch off the “house” trunk. A major advantage of this approach is that the code can refer to, in that instance, all houses, or just townhouses. It can prohibit all types of houses except townhouses. It’s an extremely supple and flexible way of working. It dovetails with the way that we talk and think about buildings and places.