"Grand Theft Auto IV" is an action-adventure game played from a third-person perspective. Players complete missions—linear scenarios with set objectives—to progress through the story. It is possible to have several active missions running at one time, as some require players to wait for further instructions or events. Outside of missions, players can freely roam the game's open world and complete optional side missions. Composed of the fictional city of Liberty City, the world is larger in area than most earlier "Grand Theft Auto" series entries. At the beginning of the game, players can only explore the first island—composed of Dukes and Broker—with all other islands unlocking as the story progresses.