Chicago is defined in large part by its geographic centrality. For decades its O'Hare Airport was the world's busiest, and it occupies a similar position with respect to the USA's rail and interstate highway networks. Not surprisingly, it's home to the country's largest convention center: McCormick Place. Seen here in this drone video by nick mcgee, the complex just south of the Loop offers 250k square meters (almost 2.7 million square ft.) of floor space. It was opened in 1960 and has been expanded multiple times.