interactive GTA IV Google Map.
"All roads are covered, except for a few on/off-ramps that weren't very interesting," writes Adam from GTA4.net. "There's around 3,000 separate panoramas which were stitched together from almost 80,000 in-game screenshots (captured with a script) and the final set of tiles consist of over a million images."
There are apparently some Hidden Easter Eggs scattered throughout the city.
[GTA IV Google Map Street View]