Four examples of recent theoretical attempts focused on the form of cities are examined in this class. Unlike many of those discussed previously, these have a strong interest in the experience of physical place and have a more complex view of the contemporary city. They see the city as a democratic institution, and require a systematic quality and a high degree of explicitness so that citizens can participate in constructing the city's form.
Kevin Lynch's work follows a trajectory from his interest in the perception and cognition of city form and image (image, remember, is identity, structure and meaning) to setting out the elements of a theory in his later work. In this work he aims to connect prescriptive, normative ideas to explanatory, descriptive propositions through a series of five performance dimensions: vitality, sense, fit, access and control; and two meta-criteria, efficiency and justice. He postulates these dimensions as ranges rather than standards which can be specified more precisely over time through experiment as in the development of modern science. This requires optimism about human beings' capacity to learn: "the city is not the manifestation of some iron law but rather part of changing human culture and aspiration." A glimpse of these performance dimensions in practice are detailed in "A Place Utopia" within the collection of his last writings.
In Christopher Alexander's work there is also a trajectory of ideas about city form passing through optimization, sustaining human contact, complex structures ("not a tree"), and patterns and rules of urban growth. Alexander's normative view requires a city to be formed by the application of small-scale, commonly understood fields of spatial and social relations. Such patterns have lost their meaning in modern cities, he claims, only to be revived by an explicitly shared new language similar to the widely communicated language of science. Alexander provides the beginning documents for such a language to be built systematically by subsequent practice, experiment and learning. His latest work has focused on the practice of city design, accentuating the need for rules of piecemeal growth, coherence and wholeness, the mixing of functions and sizes, and, above all, the creation of a deeply held sense of feeling. The work of John Habraken follows many of Alexander's tenets of process but does so more thoroughly and with less interest in specifying the particular form of the outcomes. Agreements are the basis of the city's form and consensus on a particular site can be reached by different parties even if they disagree on other matters. Constructive participation can be organized in a city according to levels of agreement: at the level between building and city, the appropriate level is a "tissue," the recognizable spatial patterns and repetitive features of which is a "theme." Through such clarification the city can be properly constituted as it once was, according to Habraken, before the advent of specialized professionals.
Perhaps the most widely applied of the propositions that deal with the morphology of cities is the space syntax studies of Bill Hillier. Regarding the city as a network of related spaces, this work focuses on their geometrical interconnectedness and the consequent passage of pedestrians along routes and their presence in public places. Correlating concepts such as connectivity and integration result in measures of high or low intelligibility: high intelligibility correlates the presence of people (and associated behaviors such as the absence of crime) and the spatial pattern. Such principles have in recent times been applied to a variety of practical situations, such as the design of housing and public places.
Alexander, Christopher. A New Theory of Urban Design Oxford University Press, 1987, pp. 14–5. ISBN: 9780195037531. [Preview with Google Books]
Fig.7 from Habraken, N. John. "The Control of Complexity." (PDF - 2.4MB) Places 4, no. 2 (1987): 3–15.
Fig. 1, 4, 5, and 7 from "From Research to Design: Re-engineering the Space of Trafalgar Square."
Martin, Leslie. "The Grid As Generator." (PDF - 1.2MB) In Urban Space and Structures. Edited by Lionel March and Leslie Martin. Cambridge University Press, 1975, pp. 6–27. ISBN: 9780521099349.