The BANA TG Guidelines committee did not discuss the direction to which fold-out maps should unfold, i.e. open to the left or open to the right. If the map will take up both pages and the multiple page keys will follow on subsequent pages, I don't think it should matter whether the map folds out to the left or folds out to the right. It might make more logical sense to have the map unfold to the left because it is a single sided transcription but I can't find a "rule" to support that position. I've checked with the TG Guidelines and there is no suggested direction. It would be important to be consistent within the transcription. If you were going to have 3 fold-out maps, they should all unfold in the same direction.
Diane