The paper states that most applications of parametric modelling to architecture and urban design fall into one of two strands of either form for formis sake, or the negotiation of environmental concerns, while approaches which allow scenarios to be easily tested and modified without the application of complex and expensive technologies are mostly absent, although they seem appropriate in urban design. A survey of existing approaches confirms the statement, and an example of the application of basic knowledge of geometry and parametric thinking to urban design forms the argument of the paper. The pros and cons of this simple approach is discussed, and the paper concludes, that while it does not represent a suitable solution in all cases, it fills a gap among the existing approaches to parametric urban design.