Someone seems to have gotten his hands on the GTA IV map, as can be seen here: map revealed?
It looks really authentic so I think it's the real deal. However, the pictures will probably be removed soon due to Rockstar's request so if you want to keep studying them, be sure to save them. Strangely, the site I got this from doesn't have one mention of this in their news section even though they're always first to add new facts. Rockstar probably contacted them and asked them to not post this in the news section, as it is the biggest GTA community on the web.

In a way, I'm a bit dissapointed that I got to see the map early. But I just couldn't resist to have a look I haven't zoomed in though, I just looked at the thumbnails due to my newfound principles and respect for Rockstar and I won't have a good look at the map before I have the game in my hands. Be amazed over my willpower