This article uses info from WD Wiki
Chicago is the largest city in Illinois and the third largest city in the United States. It is also the main setting of Watch Dogs. It is home to the Central Operating System (CTOS) which began citywide use in 2011.
The majority of the city has experienced urbanization and has been largely developed to accommodate business and inhabitants. The city's infrastructure is controlled by a computer system known as CTOS. The operating system software controls transportation, the Crime Prediction System technology, telecommunications, blockers, drawbridges, and much more. Aiden Pearce can hack the system to control all of these functions.
Rural areas also appear to the northwest in the Pawnee district and less central areas of the non-game map.