Abstract
Walk the slums of Dhaka, in Bangladesh, or Accra, in Ghana, and it is not difficult to see how the urban environment of poor countries could be responsible for bad health. Walk north from Manhattan's museum district to Harlem, or east from London's financial district to its old East End, and you will be struck by the contrast between rich and poor, existing cheek by jowl. It is less immediately obvious why there should be health differences between rich and poor areas of the same city. It is even less obvious, from casual inspection of the physical environment, why life . . .