@IdleRich fun fact until regulations were relaxed in the 70s City buildings were not allowed to be taller than the height of the Fire Service's longest ladder. Spires and cathedrals apart of course.
There is also a thing about sight-lines though... was still present in the early noughties I believe. And in some places about flight-paths into the airports too.
Did anyone read that amazing article about NY a year or two back? The gist of it being that you own automatically a certain amount of space above your property but these spaces can be traded. So if you want to build higher you can buy some "air space rights" from another guy who isn't planning to go up higher. I suppose the idea is that however much is traded, the total amount of the sky that is full can't go above a certain amount - although obviously where that falls down is that some buildings and heights in certain areas have a bigger effect than others.
Also, cos it's traded by volume, if you build thin, you can go up higher which is why you've got more and more of those ridiculous/cool (depending on your perspective) pencil thing sky scrapers.
So this is apparently the world's most slender tower (I guess that means the ratio of height to cross-section).