> wouldnt it need to include walls?
I suspect it is input to some algorithm - which can adjust the outside walls, and perhaps have other variations (or it the 5x5 data may have nothing to do with the acre layout)
FWIW: I gave up looking at it a long time ago. The static data isn't obvious.

If interested, you'll need to disassemble the code to figure out how it is used
(tricky to find with runtime breakpoints since this is only used at the very start of the game)