Chicago, the "Windy City" as it is commonly referred to, boasts 2.7 million residents and is the third most populated city in the United States. Extending across the Chicago and Calumet rivers, the city covers an area of 60,000 hectares and sits 176 meters (578 feet) above sea level on the southwestern shore of Lake Michigan. At 190 km wide and 495 km long, Lake Michigan is the fifth largest body of fresh water in the world. Home to O'Hare International Airport, the second busiest airport in the world, Chicago has become the international hub for finance, commerce, industry, technology, telecommunications, and transportation alike. Chicago boasts 77 vibrant neighborhoods, attracting an estimated 40 million visitors annually.