sounds like the perfect spot to put a control
Maybe, maybe not. The ISSOM standard is very clear that the map should represent a 2-dimensional space. The symbol set does not adequately provide for multiple levels beyond trivial bridge and tunnel structures. On
the control referenced by Ian (#6), the space is made 2-dimensional by the fact that there is only one legal way into the control from the north (shown by my route). You could go under the deck and cut through the out of bounds area and up the stairs, but that's not a mapping issue. I thought this control was fair, and didn't even mind that there was an illegal fix for people who blew it because they would still lose time to the optimal route. However, if both routes were legal, it would have been very important that the clue indicated that the control was on top of the deck and not in the tunnel (I would have used "paved area, on top"). It also would have been important that the tunnel was actually shown on the map (the current version gives no indication that you can go under the deck, but that's not a problem because of the out of bounds).