I am standing at the edge of a big roundabout near the centre of Leicester, an industrial city in the English Midlands. I'm trying to get to the Asian supermarket on the other side, my favourite place for food shopping, when I am in the city, which these days is fairly often. It's a muggy summer's afternoon, and the traffic is intense, roaring around me, and above me on an elevated flyover, making conversation difficult. It's a struggle to get across the road, so I have time to take in the surroundings. Around me are the surviving brick fragments of the Victorian industrial city, grimy but unexpectedly handsome, some low-rise social housing in the postwar Swedish style, and hard by the flyover, a twenty-storey modernist high-rise, built of a piece with the road scheme. It is a place no one would describe as beautiful, but I have got to know it well, and lately (and somewhat self-consciously) I have started to take pictures of it because it is, in its peculiar way, an extraordinary sight. A bizarre amalgam of things, it is something that no one would have consciously built in its present form, or could even have imagined, a century ago. Why is the traffic roaring over my head at fifty miles per hour? Why does that housing look like it belongs in Gothenburg? How have those Victorian factories survived, and what are they now for? Why is the supermarket that shade of green? Why is it so hard to get across the road? These are good questions. We habitually pass through places like this wherever they are in the world (and this fragment of Leicester could actually be anywhere, from São Paulo, to Singapore) but we rarely take them seriously, or spend any time looking at them. We should, because areas like this are what our cities mostly are. But why, if we wouldn't deliberately set out to make cities like this, do they look like this? Why do cities look the way they do?

There aren't any straightforward answers, in part because when we think about cities, we habitually think they must have been designed. We want to attribute London to Christopher Wren, Barcelona to Antoni Gaudí, Chicago to Ludwig Mies van der Rohe, or São Paulo to Lina Bo Bardi. We're habituated to think of design and intention. But even if these individuals built great things in cities, they are no more than fragments of the whole: cities rarely have designers as such, however much we might want that to be the case. Instead, this book argues, cities are the outcome of processes that may have spectacular visual effects, but which are in themselves generally unconscious. Design responds to processes, such as the demands for housing, or for places for people to work, or for buildings that make attractive capital investments, to pick examples of typical urban processes, as well as one covered by this book. And design is often trying to ameliorate the effects of processes – think how much architecture is about mitigating changes in, for example, the workplace. But cities, and the way cities look, are largely the result of processes that design doesn't, and can't, control, much as it might like to. Of course, that is much less true of planned economies – for example, in North Korea now, or the USSR in the 1950s, or even, briefly, in Britain's postwar new towns (see Harlow, or Milton Keynes, or Cumbernauld). It is, however, certainly true now of the global cities of the world, which is to say those cities that understand themselves to be part of the global economy, or which aspire to be part of that economy. ‘Global’ means not only financial and informational networks, but also, importantly, the projection of ‘global-ness’ to the rest of the world, a promotional process in which the way a city looks matters a great deal. (For more on this, you could start with the work of Saskia Sassen, a sociologist of globalization.¹)

Design, of course, routinely struggles with this problem of process. ‘Design’ means architecture to begin with, the professional discipline most commonly associated with city building, and it means all the professions allied to, and overlapping with, architecture. It means landscape architecture, when we are thinking of the open spaces of cities, their parks and public spaces, their streets and squares. It means town planning, which, depending where and when it has been practised, can be a highly ends-oriented, practical profession focused on the provision of primary services, or one astonishingly short on detail, bordering on art (Lucio Costa's 1957 plan for Brasília is a great example of the latter). Design can also mean the contemporary subdiscipline of ‘masterplanning’, a kind of urban public relations aimed at attracting capital or boosting a city's standing in some real or imaginary urban competition. Design certainly means engineering, in terms of both the engineering of buildings without which they would not stand up, and the major structures of cities, like bridges or highways, or towers. Some of the latter inhibit a grey zone bordering on architecture – think of the work of Gustave Eiffel of the eponymous Tower, or, more recently, the work of Santiago Calatrava, who has made bridges into a form of public sculpture. You can find all these disciplines in more or less the same place, educationally and professionally, and in multinational practices, like Foster and Partners, where you find them as all part of the same multidisciplinary package. The firm can, and often does, provide all these design services.

The design professions have some important things in common. They make it possible to believe in a designer, someone who literally draws, and through drawing makes things come into reality. That is a very powerful idea, endlessly reiterated in photographs of architects or planners at desks, drawing. I met the great Brazilian architect Oscar Niemeyer in 2001 when he was already 93 years old (he died eleven years later, when he was nearly 104). He was as great an enthusiast for the myth of the designer as you could hope to find. We met in his studio, where we sat at his desk, and his conversation was punctuated by sketching. I pick up a pen, he told me as he told absolutely everyone who came through the studio, ‘and a building appears’ – and that magical transformation, effortless lines in pen and ink becoming concrete, seemingly without any intervening struggle, was what Niemeyer described to everyone in every TV interview, every press interview, every photograph. He had an engineer in the office, of course, but the process of building held little interest for him, as did (notoriously) the performance of his buildings after they had been put up. There was often a gap, to say the least, between the rhetoric of the image in the architect's hands, and the messy reality. Niemeyer's buildings, as often as they were brilliant, could also be highly impractical and poorly built. The case of Niemeyer is merely an example of a much bigger problem, of course, which is our tendency to invest too much in the myth of the designer, in their unencumbered imagination, in their ability to produce total solutions. The reality is far more complex.

So this book is, first of all, about processes – the circulation of money, the operations of political power, the changing nature of things as different as work and sex, and the impact of war and culture. The book is about the way all these processes inform the look of the city, much more than the actions of any individual. Second, it's a book about images. Cities are their visual representations as well as material realities. As much as we understand cities by the way they look in reality, we also understand them through images that we have already seen – so we can understand the modern city at night, all high-rise towers and lights as constituting some kind of romantic image (see chapter 4) because we have seen so many films that say this. Or we understand a refurbished industrial building to be culturally sophisticated, because we have now seen so many pictures of such buildings converted for creative purposes (for example, chapter 5). As tourists, we know how much images of cities condition how we perceive them, so our experience of New York or Beijing, Venice or, for that matter, Disneyworld, is a mixture of material reality and image. So when we think of the look of the city as being conditioned by process, we're thinking of it as an image as much as a material reality for the reasons above – and it is often through image, especially images in mass media forms like film, that the argument about process is best made. City designers have a stake in design, naturally enough. Filmmakers, artists and photographers, and for that matter we ourselves, with our smartphones, aren't subject to the same restrictions, and it is their (and our) images that often best reveal the processes of the city. Put crudely, designers tell you how they would like the city to be; image-makers, at least for some of the time, are more inclined to try to tell you how it is. Of course, the best designers exemplify both attitudes. Learning from Las Vegas, the great 1972 book by the architects Robert Venturi and Denise Scott-Brown, is a radically open-minded survey of that city as much as it is a prescription for anything new.² Its openness to the actual city as much as to the imagined one is an important lesson, and one of the models for this book. Although it is about the real city of Las Vegas, it is more generally about the city as process. And thinking about the city as a process, architects would argue, explains why cities take the strange forms they do, how they evolve and change and how we as their inhabitants often have more agency than we might think. Seeing cities as processes arguably downgrades the role of the designer, and not all architects will be pleased by this book's emphasis. But understanding process not only explains why cities look the way they do; it might, in the end, help us make better cities.