sydney is a world city, its up to you if you want to call it 'secondary' or not, its not really that important an issue. the major world cities are tokyo, new york and london mainly one for each major region (brittan and europe, asia and the pacific and america). the paris thing does depend on the author, but that also is not all the most important thing to be worried about, you can mention that if you want to so not. sydney is the main world city for australia, new zealand and the pacific islands, connecting each of the contries to the world network. having all the little details are handy and do add marks IF used appropriately so know why and how the extra facts fit in.
the 3 major ones help to link the minor ones in their region. we had this whole thing going with 3 major hubs centred at tokyo, new york and london.
michiru, the culture isnt the defining factor of world cities, its the economics, connectiveness with the global market etc. tokyo definately has that.
still waiting, i think you're correct on that, i can't quite remember but it sounds right, you seem to have the idea.
zenger69, paris is a world city, and quite an important one at that. dont confuse the idea that the 3 major ones are the only world cities, i think this is what you are doing.