IGN is giving people the opportunity to Google Map their routes in Liberty City, specific to each mission you might go on. You can also use the interactive map to find restaurants, hospitals, etc. Each mission on the map is tied to a "start" button, which will allow you to see the name of the mission, and the route you must take to accomplish it.
We are nothing but impressed when it comes to the level of immersion that Grand Theft Auto IV has dished out, both within the game and without. This is just another excellent level of coolness to explore in what has become a vast undertaking. Go and plan your routes, or show a new and better way to accomplish one.
IGN: Liberty City Map