What are the names of airport which is the source for the most number of flight routes?
SELECT T1.name  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
source for the most number of flight routes refers to MAX(COUNT(routes)); names of airport refers to airports.name;