How do you destroy and/or take possesion of a city on an island that's the size of the city?

What I mean is since the city take up the whole island, I'm unable to land units on it....

I encountered the english city of coventry that was on a one tile island and had the same problem.The first unit that can do this is the marine, it has the amphibious abiltay which means it can attack something directly from a transport, also some units have an amphibious promotion that you can get for them. But the marine(and the navy seal i think) start out with the amphibiuos trait.

All units can attack straight from a transport - the amphipious trait only eliminates the penalty for doing so.

sorry mate, im still so used to civ 3.

Great, thanks guys!