Emergent urbanism

by Mathieu Helie, graduated of the Institut d'Urbanisme de Paris, Universite Pantheon-Sorbonne and Concordia University.

"[... ] Emergence is a form obtained as a result of following certain processes. The opposite of emergence is design: it is a form conceived by a designer which will be used as a blueprint for its realization.In emergence, form is the result. In design, form is the starting point. [... ]"

"In a traditional spontaneous city, 100% of the surface is initially a network structure, open land. From this surface the best paths are selected to fit the networks that are emerging, and the leftover space is progressively built upon. Starting with a completely open, fully-connected land structure, the city’s design can consist of a purely negative process by placing constraints on construction over important paths. In this way the street structure and hierarchy becomes an evolved structure that matches the history of its networks, and the placement of buildings and uses is also an evolved structure that matches the flows of movement.Over time these paths are paved and upgraded, and important junctions of paths become the central open space of the city. The central square of a spontaneous town can be explained as the remainder of a fractal process of subtraction, with the most underused part of the spatial network being removed at each additional step of feedback until no further network subtractions are possible.

An emergent city similarly begins with a network structure, although one that is much more sophisticated than open land. In modern design the typical asphalt street produces a network that is suited particularly to automobile networks. [... ] Some efforts have shown that pedestrian networks can emerge from modern design. One example is the three-story deck of the La Défense business city in Paris, which contains parking but also regional rail and subway links, as well as being an open pedestrian surface. At the ends of this network structure a generative process of spontaneous development creates the actual networks of the city.[... ]

Most importantly all forms of movement must be in balance in the street design so that one type of network structure does not cut another and prevent the network formation process. (Salingaros, 1998)

[... ] Wiki systems have shown that simple freedom to create does not necessarily produce networks unless there also exists a simple interface to this network. [... ]"

"[... ]How is it possible for what is obviously a human artifact to arise as if by an act of nature? The theory of a spontaneous order provides an explanation. According to Friedrich A. von Hayek (Hayek, 1973) a spontaneous order arises when multiple actors spontaneously adopt a set of actions that provides them with a competitive advantage, and this behavior creates a pattern that is self-sustaining, attracting more actors and growing the pattern. This takes place without any of the actors being conscious of the creation of this pattern at an individual level. The spontaneous order is a by-product of individuals acting in pursuit of some other end.[... ]"

"I have argued that what makes cities different than building projects was the fact that they have to deal with change and uncertainty, and that subdivision-planned developments are economically inferior to random growth. These arguments rely on the fundamental quality of cities as systems, a property that places them in the same class as biological systems while separating them from mechanical systems. This quality is being scale-free. That is to say, a city can work no matter what size it takes. [... ]"

"Christopher Alexander showed in A City is not a Tree that social and economic networks formed complex semi-lattice patterns, but that people who observed them limited their descriptions to a simple mathematical tree of segregated parts and sub-parts, eliminating connections in the process. [... ]
These social networks grow more complex with increasing building density, but a forced increased in density does not force social networks to grow more complex. [... ]

The built equilibrium
Although they may appear to be random, new buildings and developments do not arise randomly. They are programmed when the individuals who inhabit a particular place determine that the current building set no longer provides an acceptable solution to environmental conditions, some resulting from external events but some being the outcome of the process of urban growth itself. It is these contextual conditions that fluctuate randomly and throw the equilibrium of the building set out of balance. In order to restore this equilibrium there will be movement of the urban tissue by the addition or subtraction of a building or other structure. In this way an urban tissue is a system that fluctuates chaotically, but it does so in response to random events in order to restore its equilibrium. This explains why spontaneous cities achieve a natural, “organic” morphology that art historians have had so much difficulty to describe. [... ]
Modern urban plans do not include a dimension of time, and so cannot enable the creation of new networks either internally or externally. They determine an end-state whose objective is to restore a built equilibrium through a large, often highly speculative single effort [... ]"

"Bill Hillier of Space Syntax is, along with Christopher Alexander and Michael Batty, part of the British old school of urban complexity researchers.[... ] He presents a theory of urban emergence founded upon two ideas. First, that circulation in a city is determined by the configuration of lines into a global hierarchy of depth, which he calls integration. Second, that activities in the city adapt to take maximum advantage of this movement, a phenomenon he calls a “movement economy.” How did he draw this conclusion? By observing that integration of lines could predict where all the major shopping streets in London are.[... ]
From this knowledge, we can arrive at a paradigmatic definition of urbanity. A space can be considered urban if it makes maximum economy of the movement that passes through it. A city, at any scale, will be qualified as a good city if the experience of movement is not felt as a burden but as an opportunity and pleasure. [... ]"

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Posted by etienne mares / 8.2 years ago / 4252 hits