i just want to put my bit in and say that:
according to JV Beaverstock - the ranks of world cities has recently changed...
Alpha ++ = London and New York
Alpha + = SYDNEY, Hong Kong, Tokyo, etc
Alpha =
Alpha - =
Beta + =
Beta =
Beta - =
Gamma + =
Gamma =
Gamma - =
So go onto Wiki... have a look what it says because.. the ranking of world cities has changed as of last year... but main differences are that Tokyo is no longer one of 'the' major world cities (possible language barrier??) and syndey is positively moving up in the ranks (having been moved up from a beta world city - possbily because we are the first major market to open on a new day