SELECT city_name FROM city WHERE population  =  ( SELECT MAX ( population ) FROM city );
whats the largest city
[Schema (values) (types)]: | geo |  state : state_name (text) , population (text) , area (number) , country_name (number) , capital (text) , density (text) | city : city_name (text) , population (text) , country_name (number) , state_name (number) | border_info : state_name (text) , border (text) | highlow : state_name (text) , highest_elevation (text) , lowest_point (number) , highest_point (number) , lowest_elevation (text) | lake : lake_name (text) , area (text) , country_name (number) , state_name (number) | mountain : mountain_name (text) , mountain_altitude (text) , country_name (number) , state_name (number) | river : river_name (text) , length (text) , country_name (number) , traverse (number);