XKCD comic #1196 – Subways has a great map of the subways in North America linked up by some fantastic, mythical branch lines. I started collecting the actual maps for all of the subways, until I recalled that the The Urban Mass Transit Systems of North America map from Yale Professor Bill Rankin on his web site Radical Cartography (ca 2006) has already done the work. That map scales, rotates, and geographically maps the subway systems to allow for accurate comparisons. Mr. Munroe probably got his inspiration from that map!
In case you’re interested, here’s the collection: