It is increasingly recognised that cartography is a contested practice, embedded within particular sets of power relations, and that maps are bound up with the production and reproduction of social life. The author begins by emphasising the importance of these issues for considering how the city has been mapped and represented through cartographic schemes, and draws on debates around the power and politics of mapping, and contentions that maps are 'preeminently a language of power, not of protest'. However, it is argued that maps and mapping have not been entirely the preserve of the powerful, and the main part of the paper is devoted to examining some specific challenges to 'official' cartographies of the city. The author focuses on the radical art and political group, the Situationist International, and its avant-garde predecessors of the Lettrist International, who sought to appropriate urban maps and cartographic discourses and to develop a new form of 'psychogeographical mapping' during the 1950s and 1960s. The paper provides an account of their subversions, and an assessment of how their concerns might inform contemporary discussions on cartography and the mapping of urban space.