'To make sense of a city, you need to know something about the people who live in it, and the people who built it. You need to ask how they did it and why.' Most of us now live in cities. But what makes a city? Is it a place - or an idea? How should we define the city as it evolves today? Deyan Sudjic, Director of the Design Museum, decodes the underlying forces that shape the urban spaces around us, from their buildings to their names, from the power of crowds to why being a Londoner, New Yorker or Muscovite can offer a sense of identity greater than any other.