What are the names of city of airport which is the source for the most number of flight routes | Do you mean the name of city which is the source for the most number of flight routes? | Yes
SELECT  T1.city  FROM airports AS T1 JOIN routes AS T2 ON T1.apid   =   T2.src_apid GROUP BY T2.src_apid ORDER BY count ( * )  DESC LIMIT 1
name of city which is the source for the most number of flight routes refers to MAX(COUNT(flight_routes)) where flight route source matches city's airport ID;