Basically a childhood railroad that consisted of 2 loops and a couple of sidings on a single 4 x 8 sheet of plywood was expanded bit by bit to become a 12 x 8 mamouth. It is a basic U shape.  The original 4 x 8 contains the town and several businesses located along sidings.  The connector piece contains all of the industry and many more sidings.  Finally the other 4 x 8 is made up of the engine storage, complete with turntable, and also the yard.