Question: what are the main hubs for southwest airlines
Answer: Chicago; The Windy City; City of Chicago; City of Broad Shoulders; Chitown; The Queen of the West; City by the Lake; Chi-Raq; Chi-Town; Chicago, Illinois; The Second City; Atlanta; The A; Atlanta, GA; Terminus; The ATL; The Big Peach; Hotlanta; Atlanta, Georgia; Denver; Queen City of the Plains; City and County of Denver; Queen City of the West; Denver, Colorado; Mile High City; Baltimore; City of Baltimore; Baltimore City; Baltimore, Maryland; Charm City; Midway International Airport; MDW; Chicago Air Park; Chicago Midway Airport; Midway Airport; Chicago Municipal Airport; KMDW; Chicago Midway International Airport