Our mental pictures of cities are generally determined by maps – flat projections that suppose a viewpoint high in the air, completely removed from the chaos of the street. This gives rise to a horizontal picture of the city, where all spaces are arranged as if flattened out on a surface to be apprehended at a glance. This may be useful in navigating urban space – getting from A to B, or more likely A to Z, but it conceals another view of the city, the vertical view. If we were to cut a section through a city like London, it’s vertical structure would be revealed – from the highest hills, church steeples, and office blocks, to the vast underground spaces of the Tube, sewers, utility tunnels and subways. Traversing a city like London often involves just as much vertical as horizontal movement. Yet picturing this in our minds is often very difficult, because we do not conceive vertical space very easily. As a consequence, our constant ups and downs in the city become blanked out, consigned to the drab world of commuting and only noticed when things go wrong. Yet, apprehending our vertical movement – perhaps, even mapping it – would undoubtedly lead to a richer understanding of the city and its complex web of spaces.