In your latest book «Vertical» you claim that our world can no longer be read as a two-dimensional map. Why?
Because the 2D map only allows the surface level to be understood. Urban life, whilst focused on the surface, occurs within, and is mediated through, a three-dimensional volume of space from the orbits of satellites through the tallest towers to the complex subterranean world beneath the surface right down to the deepest  mines (which delve four or five times further into the ground than the tallest skyscrapers go up). Anyone using traditional 2D map in the world most verticalised city – Hong Kong – quickly realises that it’s next to useless because it fails to show the complex three-dimensional structures, walkways, lifts and spaces structured within this complex volume.

In a future digital world we won’t have to leave our houses to meet with friends or to buy groceries. Which role will the spaces and layers of a city play by then?
Cities and physical spaces will always be the pivotal domains to support and nurture all the things that can not be digitally mediated. Despite the growing power of telecommunications, activities involving trust, sexuality, food, fashion and live music/art/events/sports remain fundamentally based in physical urban places. Indeed, digital media, rather than simply replacing urban places, merely “remediate them”. That is, the body, the street, the neighbourhood, the car, the city etc. are merely reconfigured in the ways in which they function to sustain cities through the new possibilities that new media offer. Uber is one example.

You are describing a “class war from above” where the privileged have seceded upwards into residential towers, hotels and roof gardens. What does this mean for the real estate industry?
The intensifying inequalities in the world's most important “global” cities, combined with the surplus investment that the world's super-rich have to invest and the premium that can be charged for penthouse spaces, are combining to make the real estate industry focus heavily on the super-rich. Certainly in London and New York, the profitability of developing “super-prime” housing towers for the world's ultra net worth individuals, often as investment vehicles to be consumed from afar, is having very garret consequences for the housing of those on lower incomes who are facing a worsening housing crisis despite the procreation of building projects in the city that are ostensibly about “hoping”. But these elite, luxury towers house capital rather than people. Their owners rarely visit them and many are permanently unoccupied.

Is there a vertical limit to cities?
Interestingly, engineers now argue that it is elevators technology that currently limits skyscraper height. New elevators based on carbon fibre or magnetic propulsion will allow elevators to travel in one go along elevator tracks that are 1 to 1.5 km long. Currently, the limit is around 500m because of the weight of steel cables in traditional elevators. 1.5 km towers are already being designed.

At the 13. European Trend Day Stephen Graham will take a vertical a vertical look at urban life. Sign up now!