Let me begin with an urban nightmare masquerading as retail dream. Bluewater is a mega-mall shopping complex outside London, and a vast experiment in consumerism. A £375m, 240 acre, self-contained world replete with not only 1.5 million square feet of lettable space spread over 325 fashion shops and other retail outlets; there are three full-blown leisure villages offering multi-screen cinema, outdoor plazas, food courts, night-time bars, public art works and a rock-climbing wall. It is an internalised, predictable, controlled, safe and sterile arena. It is a place that suggests that we are only citizens in so far as we shop or consume. It is a place that suggests that we know what we want, and we know where to find it. Bluewater is a place where there are no surprises.

Let me begin with an urban nightmare masquerading as retail dream. Bluewater is a mega-mall shopping complex outside London, and a vast experiment in consumerism. A £375m, 240 acre, self-contained world replete with not only 1.5 million square feet of lettable space spread over 325 fashion shops and other retail outlets; there are three full-blown leisure villages offering multi-screen cinema, outdoor plazas, food courts, night-time bars, public art works and a rock-climbing wall. It is an internalised, predictable, controlled, safe and sterile arena. It is a place that suggests that we are only citizens in so far as we shop or consume. It is a place that suggests that we know what we want, and we know where to find it. Bluewater is a place where there are no surprises.

It's far from unique - merely an extreme version of one of the most powerful visions currently promoted for the future of the city: that the city is, above all, else a place to shop.

How can we offer a different view of the city? Where can we find practices and spaces that are less docile, less passive, more creative in their engagement with cities? For myself, this has taken the form of a study of skateboarding. Skateboarding is an activity that is culturally critical, and which above all is performed in direct relation to architecture and urban space. It therefore shows how there might be great potentials in cities and architecture that are as yet largely undreamt of by architects, planners and urban managers.

Skateboarding is not, of course, a purely bodily activity, devoid of social meaning and significance. Skaters are predominantly young men in their teens and early twenties, with broadly accommodating dispositions toward skaters of different classes and ethnicity. Despite its lack of real criminal activity, skateboarding has become increasingly repressed and legislated against, not by national or federal laws but by a series of local reactions aimed at suppressing that which is different (and misunderstood). Such laws add to the anarchic character of skateboarding, part of its continual dependence on, as well as struggle against, the modern city.

What then to make of this study of skateboarding? Where does it leave our understanding of cities and architecture in general? In the most general terms, we can begin to delineate an understanding of cities that does not focus solely on things, effects, production, authorship or exchange. The study of skateboarding shows how cities also involve various machines and tools, everyday spaces, imaginative experiences, city mapping social identities and urban terrains.

Cities do not always have to be the place of consumption and genteel civilisation like the shopping mall at Bluewater. Cities can also be composed of all the disparate activities that people do in cities. That is, they are cities of shouting, loud music, sex, running, demonstrations, subterranean subterfuges. They are the cities of intensity, of bloody-minded determination, and getting out-of-hand; they are the cities of cab ranks, boot sales, railway arches and street markets; they are the cities of monkish seclusion, crystal-clear intellectualism, and quiet contemplation.

What skateboarding, and all the myriad urban practices of the city tell us, is that we need to need to celebrate three things: different peoples, different spaces and different ways of knowing the city. We need to celebrate the people of different backgrounds, races, ages, classes, sexuality, gender and general interests, all of whom have different ideas of public space, and who subsequently use and make their own places to foster their own identities as individuals and citizens.

And we need, therefore, different kinds of spaces. Beyond the shopping mall and the piazza, cities need hidden spaces and brutally exposed spaces. And we need practices like skateboarding, all of us, whether we skateboard or not.