Which is irrelevant for Marvel Comics, because instead of creating fictional cities, the vast majority of the events of the Marvel Universe take place in New York City. Well, at least they take place in the Earth 616 version of New York City, and to try to bridge the reality and fiction, the comic industry fan mag Wizard has put together a map of important locations in the Marvel Universe New York City. Marvel themselves apparently did something similar a few years ago, and fans, of course, have done the leg work and taken photos of the real-life NYC equivalents.
Oddly enough, on the whole, I find Marvel's NYC far less interesting than Gotham or Metropolis. There's less room to play with, and while DC's fictional cities each have their own mythologies, Marvel very rarely makes use of the history of NYC in its storytelling. (It's worth noting that NYC actually exists in the DC Universe. Nightwing is hanging out there, at the moment.)
(Via Kottke, shared by J. Lavolette.)