Chicago and Houston rank third and fourth, respectively, in the list of U.S. cities by population. San Francisco, with fewer than 1 million people, ranks 13th. Atlanta, admittedly, ranks 40th.
if you prefer metro areas to population within city limits, then Chicago/Joliet/Naperville and Houston/Sugar Land/Baytown rank third and sixth, respectively. Atlanta/Sandy Springs/Marietta ranks 9th, while San Francisco/Oakland/Fremont ranks 11th.
Not knowing basic U.S. geography nor knowing how to use Google to look up facts about basic U.S. geography = fails.