This iteration is only loosely based on New York, and incorporates elements from other U.S. cities, such as Philadelphia, Detroit, Boston, Chicago, and Baltimore.[56] The city encompassess three main islands, which are gradually unlocked as the game's storyline progresses: Portland (based on the industrial areas of Brooklyn and Queens, with additional elements from Manhattan and Long Island), Staunton Island (based mostly on Manhattan), and Shoreside Vale (loosely based on North Jersey, The Bronx, Staten Island, and Upstate New York). The islands are connected by road bridges and an underground tunnel system. A tunnel leading out of Liberty City can be found in Shoreside Vale, but it is inaccessible to the player.