Chicago is a center for finance, culture, trade, industry, education, technology, telecommunications, and transportation. It is one of the largest markets of the world. The O'Hare International Airport is the fifth or sixth busiest airport in the world and first or second in the United States. The region has the largest number of federal highways. It has many railroads too.Globalization and World Cities Research Network lists Chicago as an alpha global city. The Global Cities Index ranked Chicago seventh in the world in 2017. The Chicago area generated $689 billion in 2018. It has a very diverse and balanced economy. Chicago is home to several Fortune 500 companies, including Allstate, Boeing, Exelon, Kraft Heinz, McDonald's, Mondelez International, Sears, United Airlines Holdings, and Walgreens.