The third great normative model, which claims that the city is analogous a living organism, is more recent and arose from the growth of biology in the eighteenth and nineteenth centuries. Its advocates are often critical of other models. For instance, the German urbanist Hans Reichow in his 1948 book on organic city planning, architecture, and culture condemns "simple grids" or "products of the Grand Manner" as "static." The theory of the organic city rests on a number of assumptions about the nature of organisms. Among these is the assertion that an organism is an autonomous individual, and that it has a definite boundary and is of a specific size. It does not change merely by adding parts but through reorganization as it reaches limits or thresholds. It contains differentiated parts but form and function are always linked. The whole organism is homeostatic, self-repairing and regulating toward a dynamic balance. Cycles of life and death are normal to organisms as is rhythmic passage from one state to another. From this flows the notion of the form of the organic city. It is a separate spatial and social unit made up internally of highly connected places and people. A healthy community is heterogeneous and diverse. The micro-unit is the neighborhood, a small residential area, which was defined by Clarence Perry in 1929 as the support area for an elementary school to which children, the most vulnerable of the human species, can safely walk. Like organisms, settlements are born, grow, and mature, and if further growth is necessary, a new entity has to be formed. Thus there are states of optimum size, beyond which pathological conditions ensue. Greenbelts not only ensure intimate contact with nature but also enclose healthy growth. This model has typical physical forms, such as radial patterns, anti-geometrical layouts, and a proclivity for natural materials. Often the organic idea is extended regionally to connect settlements to valleys, trails, and other extended natural systems. There is an attraction to small-scale modes of production or services as opposed to large-scale synthetic processes. Often the model aligns itself with a socio-economic philosophy that sees increases in urban value as the result of communal rather than individual endeavor.
Three cases are examined to locate these principles in practice. In the first case, the ideas and projects of Patrick Geddes are surveyed including his synoptic vision (folded paper, the Valley Section, and plan for the Hebrew University), the need for civic inclusion, and the benefits of conservative surgery and cultural retention (Indian projects). The second case covers the work of Ebenezer Howard and his attempts to balance country and city, the garden city idea in the plans of Letchworth and Welwyn Garden City, and the details of density, landscape and site planning in the association of the organic with the picturesque. The third case covers the regionalism of the American plans of the early twentieth century, the ideas of heterogeneous balance and Georgian socio-economic philosophy in the urban projects of Stein and Wright.
Epochs of development in New York from Report of the Commission of Housing and Regional Planning to Governor Alfred E. Smith, 1926.
Fig. 31, 33, 35–6, and 39 from Changing Natures in Dynamic Urbanism.
"Tennessee Valley Authority v. Hill." The Snail Darter Case. 437 U. S. 153, 1978.
The Valley Section (Patrick Geddes); plan for London, England (Eliel Saarinen); plan for Washington D.C. (Victor Gruen); plan of the University of Jerusalem; plan for Balrampur, India (Patrick Geddes); plan for Manchester, England (Friedrich Engels); Golders Green, Adelaide, Welwyn Garden City, Sunnyside Gardens (England); Central Park (New York, United States); Chatham Village (Pennsylvania, United States); Greenbelt (Maryland, United States)