Calling for new urban planning visions and tools
Last week, Michael Mehaffy presented in our Habitat 3 class at Stanford. He called for new models and new urban planning tools to achieve the goals delineated by the New Urban Agenda. To support his call for actions, Michael Mehaffy mentioned authors who influenced the way we think about cities, notably the opposition between Le Corbusier’s City as Machine and Jane Jacobs’ City as a living being. On the one hand, the city needs to be engineered by a grand architect to get the most efficient urban systems. This means getting rid of the apparent disorder created by inhabitants through incremental growth. On the other hand, Jacobs supported a vision of the city as fundamentally social. People’s interactions and influence on street designs and activities are the fabric of the city more than the brick and mortars of buildings.
In 1965, with his essay “the City is not a tree”, Christopher Alexander added a new dimension to this debate by using concepts from mathematics, trees and semi-lattices, to describe the complexity of traditional compared to modern cities. Trees are sets of elements that have no overlap, whereas semi-lattices allow for overlaps between sets [1].
Figure 1: Christopher Alexander's representation of semi-lattices (a & c) and trees (b & d). Source: Alexander, C. "The city is not a tree", 1965.
Alexander called out the very way humans think, the need to separate elements and order them by categories, as leading to bad city planning. Indeed, Alexander proposed that inhabitants’ experience of a city is rich and adaptive because elements of the cities can be rearranged in endless combinations of sets. He gives the example of a traffic light next to a drugstore in Berkeley. This combination of apparently heterogenous elements give rise to interesting human activities: the drivers watch magazine covers and buy newspapers while waiting at the traffic light. However, the apparent heterogeneity of the elements “drugstore” and “traffic light” might have prompted planners to separate these two activities. They would be handled by two different designers and be separated spatially through zoning codes.
Alexander critiques modern city plans for separating urban elements per a rationale that might seem logical conceptually, but that in practice prevent new combination of elements essential to urban social life. This dichotomy is visible when one maps out where people live and where they go to a school or a club for example. People’s movements are almost never circumscribed by their neighborhood limits. In addition, where some activities should be located cannot be optimally decided based on the type of activity it is. It would prevent new relationships between activities and people to appear and adapt to inhabitants’ needs and habits.
Finally, the idea of overlap between sets is extended to human networks and notably City Government. Alexander argues that even though the organizational chart of City Government is a tree, people do not necessarily interact with each other solely based on hierarchy. Convergence of interests between people from different sets, or need for expertise for specific new problems might bring together people from different departments and experience level.
These examples lead to think about the need for a polycentric governance and plans that allow people to come up with their own new sets of urban elements adapted to their evolving needs and habits.
One example where top-down design often fails is public space. It is hard to predict exactly what path people will most often take and what activity will be most important to them. I was recently struck by such an example. At a busy intersection, there was a large flowerbed at the corner of two roads. It completely separated the roads from the shops and the sidewalk. This should have created a small plaza protected from the noise of the road in front of the shops. It seemed a good design idea. However, the small plot bear the mark of footsteps showing 2 clear (informal) paths. These were the fastest routes for pedestrians crossing both streets and trying to continue toward their destinations. I remember instinctively crossing the street and wanting to go across the flowerbed exactly where these informal paths were. I also felt really annoyed that I could not go to my destination directly but had to go around the flowerbed. Could the planner have thought of it in advance? I doubt it. It prompts to recognize that places need to adapt as people’s activities and movement change.
Alexander admitted in his essay that he did not have a recipe to create a plan that would be based on semi-lattices instead of trees. He did uncover the fact that categories and apparent rational organization might be the main problem of planning. Now how can one plan without categories? Maybe by leaving more space for people in cities to come up with their own solutions. An example of such community-led design is parkets. In San Francisco, residents were encouraged to reconquer some of the parking spots on the street and transform them into small parks.
The Urban Age talk at Habitat 3 envisioned a large scale planning paradigm shift. Saskia Sassen, Richard Sennett, Joan Clos and Ricky Burdett followed this line of thought and suggested that we plan cities that are “porous”, “complex”, and “incomplete” [2].
Figure 2: Noriega Street Parklet-Matarozzi Pelsinger in San Francisco. Picture from the website inhabitat.com in an article on parklets by Bridgette Meinhold from 12/19/2012 [3]
[1] Full text of Alexander's essay: http://www.bp.ntu.edu.tw/wp-content/uploads/2011/12/06-Alexander-A-city-is-not-a-tree.pdf
[2] More on the Quito Papers here: http://citiscope.org/habitatIII/news/2016/10/quito-papers-intellectual-counterpoint-new-urban-agenda
[3] Source of the picture: http://inhabitat.com/noriega-street-parklet-is-a-succulent-meeting-spot-crafted-by-the-community-in-san-francisco/noriega-street-parklet-matarozzi-pelsinger-1/