The Climate Change Project, City of Mississauga
The machine-learning algorithm processes a training set composed of images of grafted fruit trees. It watches as gardeners and farmers cut underperforming-but-still-sturdy trees down to a stubby rootstock, trim healthy shoots from more desirable trees, insert those shoots—or scions—around the bark of the rootstock, bandage it all up, then fashion for our Siamesed tree-twins a rehabilitative greenhouse from a plastic bag. Over time, the rootstock’s and scion’s vascular tissues grow together: they “inosculate.” And after a couple of growing seasons, the machine observes, our gardeners yield sturdier, hardier, disease-resistant trees that produce more fruit, at much younger ages, than their unadulterated kin. The machine has learned to graft, and it’s observed which methods generate the greatest yield.
We then port that grafting algorithm over to the urban planning lab, where our data scientists aim to graft a healthier, sturdier, more fruitful city—an urban scion—onto some underperforming rootstock. Our planning algorithm searches aerial imagery and Street View images to identify barren waterfronts, brownfields, and blighted neighbourhoods with potential for resuscitation. It then grafts onto that urban rootstock a lattice of urban systems—pipes and cables and roads and buildings—in patterns it has learned from other successful cities (with “success,” of course, determined by the optimization of various urban indices). Over time, the root’s and scion’s infrastructural veins and arteries are sutured together. And after a few months, the urban machine is able to sustain a vibrant ecosystem of people and Dutch grocery bikes and King Charles spaniels and vegan eateries. And its yield—of data and profit—is abundant.
This is how cities are cultivated in an age in which the “science” in urban science draws more from data and computer science than from horticulture and ecology. Here, the old art of grafting is algorithmicized and engineered.
Yet cities have always been grafted terrains. Those that have sustained more than a couple generations of inhabitants bear layers of their material history. In their urban strata we find evidence of the Anthropocene: trash, construction materials, and ruins that chronicle humans’ alteration of the planet. Urban facades sport shrouds of territorial markings, official proclamations, and commercial insignia. And enduring cities that, over the course of their long lives, have been usurped by empires or claimed by colonizers often host grafted architectures and infrastructures manifesting their mixed lineages—their entangled roots and scrambled genetic codes.
The term graft derives from the Greek graphein, or stylus—probably because those scion shoots looked a lot like writing implements. The city is grafted in this graphic sense, too: it’s a polyglot palimpsest of codes and scripts and plans. If we trace its lineage all the way back to Uruk and Çatalhöyük, among the earliest large-scale human settlements, we can see that the city has long mediated between multiple modes and means of inscription, transmission, and storage: legal codes and copper cables, algorithms and antennae, public proclamations and system protocols, clay tablets and ceramic type. Over generations and millennia, urban inhabitants have grafted code to clay, data to dirt, ether to ore.
But today’s data-grafters tend to cut the rootstock off at the stump, excising all inconvenient precedent, erasing legacy scripts. A too-low tree graft makes the organism susceptible to soil pathogens. Or it can entice a scion to plant its own roots, which can’t defend themselves against infection. The scion depends on the rootstock’s built-up immunities. Similarly, when our contemporary “urban test bed” prospectors, in their pursuit of tabula rasa, uproot the foundations of the city, they forsake the immunities of experience, the accreted defenses of history, the embedded and embodied knowledges of local communities.
Yet “a city is not a tree,” as architect Christopher Alexander reminds us.11The following quoted passages are drawn from Christopher Alexander, “A City Is Not a Tree: Part I” Architectural Forum 122, no. 1 (April 1965): 58–62; and “A City Is Not a Tree: Part II,” Architectural Forum 122, no. 2 (May 1965): 58–62, https://www.patternlanguage.com/archive/cityisnotatree.html. He contrasts two urban structures: that of the “semilattice” and that of the “tree.” The “organic” semilattice city is a “complex fabric,” a structure that has “arisen more or less spontaneously over many, many years.” It is thick, tough, and subtle. The tree city, by contrast, is characterized by its structural simplicity and minimal overlap among its urban units—whether zones or arteries or superblocks. The tree is the signature form of the “artificial” city, the city “deliberately created by designers and planners” to reflect their “compulsive desire for neatness and order.”
Designers and planners have supposedly evolved beyond the hubris and folly of the master-planned city. Instead, maybe they’ve merely sublimated the master plan in the machine, grafted algorithms onto blueprints. They’ve swapped neural nets for compulsive desires, automation for deliberation, sublimely exhaustive datasets for neatness and order. In the end, though, they’re still grafting city-trees. “When we think in terms of trees,” Alexander warns, “we are trading the humanity and richness of the living city for a conceptual simplicity which benefits only designers, planners, administrators and developers. Every time a piece of a city is torn out, and a tree made to replace the semilattice that was there before, the city takes a further step toward dissociation.”
Those planners’ and developers’ interests remind us that there’s yet another traditional grafting technique involved in urban development: the graft of corruption. With the rise of urban-tech companies, data brokers, and black-boxed administrative platforms, and with the spread of public-private partnerships, our newly grafted cities are even more at risk of infection. Urban inhabitants are ever more susceptible to surveillance and hacking and data-mining, while the city itself is exposed to corporate rot, and the social contract is subject to decay.
Grafting is an integral component of urban evolution. But in this newest variation on a well-rehearsed practice, we have to be wary of our new scions, those offshoots of the tech giants. And we must protect the rootstock, which is what keeps us grounded and resilient—and, at the same time, mindful of the many foregoing graftings that have produced the thick, tough, and subtle semilatticed structure of our organic cities.
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