Vanity height: how much space in skyscrapers is unoccupiable?

From the Empire State to the 1km-tall Jeddah Tower, our roundup of skyscrapers in numbers examines the race to be crowned world’s tallest buildingQuiz: can you guess the city from its skyline?In a world of ever-reducing space, a skyscraper is an efficient way to create homes and offices without too large a footprint. It is interesting, then, that so many skyscrapers are full of hot air. In the race for the biggest buildings, architects have fallen back on antennae and pointed spires &ndash