The phrase "alpha world cities" only returns 2600 hits on google, but the phrase "world cities" gives over a million. The Alpha part is merely to distinguish it as the highest tier of world cities  no offense, you can't put most of the other world cities (such as Beta cities Moscow and San Francisco and Gamma cities Jakarta and Minneapolis) on the same tier as NYC. There's a reason why a whopping 47% of americans think of NYC as "The City"! FYI, Chicago is second with a measly 4.5%.
 DragonAtma