Urban design is a creative task that demands the balancing of issues from multiple domains such as architecture, zoning laws, traffic planning, and others. As such, classic design models based on the assumption of the designer wandering through a monolithic design space guided by largely predetermined requirements turn out not to hold here, instead the designer constantly alters his point of view and will frequently re-evaluate his precepts to arrive at better or even simply innovative solutions. We are working on a formalization of this state of affairs. Instead of a global design space, the design is described in terms of perspectives between which the designer shifts during work. Design knowledge is incorporated both in the description of the perspectives and the translations that occur between them.