Then the map wrapping is disabled for that coordinate, that means, if you go to the top, you don't pop out from the bottom. Or there are 4 outer space rooms, which act like one wrapping room (go to the edge of the right room and pop out in the left room, without having two halves of
on the screen). At least, that would explain this:
However, if you go to the edge of the room and stay there, you don't see part of Viridian on one side and the other part on the other side;
Of course, this would have to be hardcoded.
I should have thought a bit better:
Consider that each byte has 64 bits and that each empty "Outer Space" room has 1 bit (not byte) of info. The whole polar dim. would have 3,403x10
38 bits, or 5,317x10
36 bytes.

It would be impossible to fit that into my computer.

It's very likely that each room, even if empty, has more than 1 bit. Perhaps 1 bit per pixel? If I'm right now, then your suggestion is the most likely.
However, if empty rooms don't have even a bit, then my suggestion might be right.
I read that thread before I registered.
Then why did you think that it's more likely to have warp lines? Did you forget about that thread when you wrote that?
EDIT: 204 replies! Maybe this will be in 1st after some time, after all!