The central problem for [architect Leon] Krier is that modernist urban planning works mainly though mono-functional zoning. As a result, circulation of people between zones by way of artificial arteries becomes the central preoccupation of the planner, generating an urban pattern that is, in Krier's judgement, 'anti-ecological' because it is wasteful of time, energy, and land [...]
Krier contrasts this situation with the 'good city' (by its nature ecological) in which 'the totality of urban functions' are provided within 'compatible and pleasant walking distances.' Recognizing that such an urban form 'cannot grow by extension in width and height' but only 'through multiplication,' Krier seeks a city form made up of 'complete and finite urban communities,' each constituting an independent urban quarter within a large family of urban quarters, that in turn make up 'cities within a city.'
From David Harvey, The Condition of Postmodernity, Cambridge: Blackwell, 1990, p. 67