The Loop is the central business district of Chicago, Illinois. It is one of the city's 77 designated community areas. The Loop is home to Chicago's commercial core, City Hall, and the seat of Cook County. The community area is bounded on the north and west by the Chicago River, on the east by Lake Michigan, and on the south by Roosevelt Road, although the commercial core has significantly expanded into adjacent community areas. As a business center, some of the corporations the Loop is home to include the Chicago Mercantile Exchange (CME), the world's largest options and futures contracts open interest exchange; the headquarters of United Continental Holdings, one of the world's largest airlines; AON; Blue Cross Blue Shield; Hyatt Hotels Corporation; BorgWarner, and dozens upon dozens of other major corporations. The Loop is home to Grant Park; State Street, which hosts a major shopping district; the Art Institute of Chicago; several theaters; and numerous subway and elevated rapid transit stations. Other major institutions in the Loop include the Willis Tower,once the tallest building in the world, the Chicago Symphony Orchestra, the Lyric Opera of Chicago, the Goodman Theatre, the Joffrey Ballet, the central public Harold Washington Library, and the Chicago Cultural Center.