This is one of those 90/10 rule things where just learning a post-it note worth of trivia covers you for over 90% of instances. I'm sure he's competent at navigating especially in the ordinary places reachable by ordinary subway ride. The corner that flummoxes me is that inexplicable void in the map. The big empty part of the subway system sandwiched between the EFMR and JMZ lines. That curious combination of Newton Creek, Highland park, an archipelago of like a dozen large cemeteries, more than a few heavy industrial zones, and freight rail tracks. I've seen parts of the map in this no mans land where numbered Ave's just straight up skip over a half dozen other numbers which I know exist elsewhere on the map. However the grid was zippered together, there is a seam in it and this is it.