Generative Methods

8/7/2019 Generative Methods

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Generative methods in urban design: aprogress assessmentMichael W. MehaffyEnvironmental Structure Research Group, Lake Oswego, OR, USA

The year 2007 marked the 20-year anniversary of A New Theory of Urban Design (1987),a slender volume by Christopher Alexander and colleagues that serves as a notablemilepost within the half-century old ‘‘design methods movement’’ in which Alexanderhimself played a seminal role. The ‘‘generative’’ design method of A New Theory focusedless upon the specification of a final form through schematic planning, and more on thestepwise process by which a form might emerge from the evolutionary actions of agroup of collaborators. In so doing, it challenged the notion of ‘‘design’’ as a progressiveexpression of schematic intentions, and argued for a conception of design as a stepwise,non-linear evolution in response to a series of contextual urban factors. In the 20 years

since, significant progress has been made to develop the insights of generativity in urbandesign, as in other fields. Some of Alexander’s ideas have been incorporated – notablyby practitioners of The New Urbanism – and some have been challenged and dismissed,including, notably, by Alexander himself. The author assesses progress since thismilepost volume – substantial, he argues – as well as setbacks and shortcomings, andsignificant opportunities still remaining.Keywords: generative methods, design methods; process; organic growth

Introduction

Just recently we passed the 20-year anniversary of the publication of a slim andinfluentialvolume titled A New Theory of Urban Design (1987). In it the mathematician,architect,

and theoretical iconoclast Christopher Alexander sought to establish ‘‘a new theory of urban design which attempts to recapture the process by which cities developorganically’’(Alexander et al. 1997, p. 2).

This organic development, writes Alexander and co-authors, ‘‘is not a vague feelingof relationship with biological forms. It is not an analogy.’’ It is, they say, a specificstructuralquality: ‘‘namely, each of these towns grew as a whole, under its own laws of wholeness’’(Alexander et al., p. 1). Alexander and co-authors then proceed to develop these‘‘laws of wholeness’’ with detailed structural logic, and to propose a method by which this

quality canbe attained again in a contemporary context – not through a conventional kind of masterplan, but through a process involving the sequential collaboration of a series of participants.We can describe such a method as generative. That is, we cannot know in advancethenature of the geometric results that will emerge from the complex process, thoughwe mayknow the general aims of the participants. We will generally avoid simplifying



mechanismssuch as large-scale diagrammic concepts, rigid typologies, or so-called ‘‘designpartis’’ (i.e.schemata), 1 especially in the early stages. Instead, the collaborating participants willtogether generate an evolving form that grows out of a complex transformation of the

existing place and its people, together with all its environmental, social, and cultural*Email: [email protected] Journal of Urbanism

factors. Such a generative process is continuous, and cannot be frozen in astandardizedmaster plan. 2

In this sense, A New Theory of Urban Design was a challenge to the very idea of urbandesign as an act of conventional schematic ‘‘master planning’’, and an assertion thatdesign

must be a continuous evolutionary response to a complex environment of urbanconditions.While the performance criteria may be clear at the outset, the designer’s role is notto specifythe final form, but rather the intermediate process that will generate that form.

Twenty years later, we can take stock of the developments since. Has anything likeAlexander’s ‘‘generativity’’ been incorporated into conventional urban designmethodologies?What of the efforts to engage citizens in participatory design processes? What of theefforts of New Urbanists to conduct collaborative ‘‘charrettes’’ and apply ‘‘manyhands’’in the production of the result?What of other efforts to incorporate complexity intodesign

strategies, or, in some cases, partially to abdicate the authority of the designer in thefaceof urban complexity (as was famously argued, for example, in Rem Koolhaas’s (1995)essay ‘‘Whatever happened to urbanism?’’).What have been the lessons learned fromtheseexperiences, and the opportunities still to be developed?We will argue that progress has indeed been made, but important opportunitiesremainto be developed. We will point to flaws in previous efforts, including Alexander’s ownmethods and assumptions (flaws that in many cases Alexander himself has alreadynoted);and we will discuss more recent efforts, their promises and drawbacks, and furtheropportunities remaining.

Generative methods before New Theory The holism described by Alexander and colleagues was not, of course, a newtheoreticalrecognition of Alexander’s team: indeed, the subject has been an active one in manyscientific fields over the last half century or so, from quantum mechanics to cognitiontoneuroscience to embryology to genetics. Alexander, the Cambridge-trained physicist,mathematician, and polymath, was well aware of these parallel trends.In fact, Alexander was one of the early pioneers of the so-called ‘‘design methods’’movement, an effort to establish systematic evolutionary methods in design, through



which a designer (or group of designers) can move methodically through the steps inadesign process, and not merely rely upon more intuitive and unpredictableapproaches,nor on rigid typological prescriptions. The field was driven by the need to cope withincreasing complexity in technological problems in the era after World War II, fueled

bythe development of cybernetics and computer software (Broadbent 1979). It wasbelievedthat the old intuitive methods of design experts were simply not reliable enough tomanagethis complex challenge. Within this field, Alexander’s work focused on the‘‘decomposition’’of a design problem, and the synthesis of the parts into a new form on the basis of various design inputs.Problems with the so-called ‘‘first generation’’ of design methods (including criticismsby Alexander himself and others) led to the development of a ‘‘second generation’’.Forinvestigators like Horst Rittel, we would need to distinguish between ‘‘tameproblems’’(which were dealt with well enough in the first generation) and the more common‘‘wickedproblems,’’ which include multifaceted problems like those that are typical at a largerurban scale. To cope with this complexity, the new methodology must thereforeincorporate an ‘‘argumentative process’’ within a network of issues. Moreover, thedesigner is no longer a solitary ‘‘expert’’ but a collaborator with the client and withotherexperts (Fowles 1977).

Yet a ‘‘third generation’’ of design method, around 1980, accelerated the emphasisoncollaborative process, and offered a model in which the designer (or collaboration of 58 M.W. MehaffyDownloaded At: 18:28 21 April 2011

designers) would propose ‘‘refutable hypotheses’’ for consideration by the client.Moreover, there need not be a single proposal for consideration; indeed, a ‘‘pluralityof views’’ was necessary (Dulgeroglu-Vuksel 1999).Alexander himself grew disinterested with the movement he helped pioneer, andceasedto interact significantly with its proponents. But his work clearly evolved in a similardirection, as he began to incorporate users in the design process, and as his methodfeatured a cycle of evaluation for testable design propositions.Alexander’s development of pattern languages was also an outgrowth of his strategytodeal with what Simon (1962) had earlier termed ‘‘the architecture of complexity.’’ His‘‘patterns’’ were in essence recurring clusters of design configuration, which could be

recombined adaptively to create new design solutions. Alexander had long noted aswellthat the structure of cities included overlap and structural plurality. His ‘‘patternlanguages’’ offered a grammatical system whereby the patterns could berecombined inredundant, overlapping ways.As noted above, all these insights had their corollaries in the scientific developmentsof that time, the understanding of the ways that complex systems exhibitedinterrelations of



their elements – and the implications for designers.Generative methods and ‘‘organized complexity’’A classic exposition of the implications of the phenomenon of ‘‘organizedcomplexity’’ forcity planners and urban designers was made by Jane Jacobs in the last chapter of herlandmark book The Death and Life of Great American Cities (1961). Its influence on

theplanning discipline in general, and on subsequent thinking about process andgenerativity inparticular, is difficult to overstate. (For example, Google Scholar lists over 2000citations.)In a remarkably prescient chapter called ‘‘The kind of problem a city is,’’ Jacobslucidly analyzed the implications of the scientific advancements that were thenoccurring –in particular, the understanding of complex systems in which a number of factorswere‘‘interrelated into an organic whole’’ (p. 432). This was important for urbanistsbecausethey needed to be sure they were thinking about the right kind of problem, and usingtheright tools to solve it.Science, Jacobs wrote, had grown in the last 400 years from Newtonian,‘‘twovariable’’science, to the other extreme of statistical phenomena, in which myriad variablesinteracted. This trend reached its zenith in the early 20th century, and powered thephenomenal growth of industrial technology in its early phases.Gradually, however, 20th-century science began to understand the realm in between,in which more than two variables interacted in important ways. This new domainopenedup ‘‘immense and brilliant progress’’ for the life sciences, which has fueled much of therevolutionary work in genetics and other fields. Indeed, since 1961, progress in thefieldhas only accelerated and delivered astonishing new revelations in embryology,morphogenesis, cognition, and many other fields outside the life sciences too. Jacobswas one of the first to spot the implications for urban design and planning.But planning and architecture, she noted, were lagging behind – still trying to treattheproblems of the city as either simple two-variable problems of simplicity (this many

jobsover here, that many houses over there) or problems of statistical populations to bemanaged, almost as files in a drawer. They misunderstood ‘‘the kind of problem acity is’’– with devastating results.

This amounted to a devastating critique on the top-down master-planning approach –from the highly influential Garden Cities movement, which sought to isolate andneatlysegregate planning variables such as housing and jobs (Figure 1), to the statisticallyinformed‘‘towers in the park’’ of Le Corbusier and other modernists, relying upon statistical

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management of family sizes and income groups into schemes that conceptuallyresemblenothing so much as giant filing cabinets (Figure 2):With these techniques, it was possible not only to conceive of people, their incomes, their





theirgenerative rules. Batty and his team have paid special attention to the properties of ‘‘selforganization,’’the tendency of systems to develop patterns of organized complexityspontaneously as a result of algorithmic sequences of activity. Just as bird flocks formlarge-scale coherent patterns from simple rules of distance followed by each bird, so

residentsof an informal city can build roads and other remarkably coherent structures byfollowingrelatively simple rules (Batty 1991, Batty et al. 1997).

These insights parallel, and clearly draw from, the rapid developments in complexityscience in general, and in particular the phenomenon known as ‘‘emergence.’’Investigatorshave been able to identify with mathematical precision the processes that give rise tocomplexstructures from an apparently simple set of rules, with useful implications for gametheory,economics, biology, physics, meteorology, and many other fields. In the fields of planning andurban design, the insights can be used to understand the relationship betweencomplex urbanform and relatively simple generative rules – like those followed by a group of actorsin abuilding process.

The significance ofHillier’s and Batty’s tools is that they have applied these insightsto theurban toolkit available to conventional practitioners, in effect to re-grow the urbancomplexity that previously existed or could potentially exist, with desirable results.Hillier’sanalytical technique in particular has been put to the test a number of times withnotableFigure 2. Le Corbusier’s unbuilt Voisin Plan forParis, which would have replaced much of thatcity’s organic fabric with neat, filing cabinet-likehousing for statistically managed populations.Figure 3. Cathedral design. A relatively simplesystem of nested centers with moderate overlap.


success. His analysis of the proposed modification of London’s Trafalgar Squarepredictedan increase of pedestrian activity of some 16-fold. The actual results of the work,Hillierreports, were very close to that prediction. 4

The publication of A New Theory of Urban Design (1987) Twenty-six years after Jacobs’s The Death and Life (1961), Alexander and colleaguespublished A New Theory of Urban Design (1987) – containing more than a strongecho of

Jacobs’s emphasis on process, and on the understanding and treatment of existingorganicwholes. To Jacobs’s insights, Alexander made several significant additions. Chiefly, hewanted to propose a methodology by which such a collaborative process couldproducegeometries that had the characteristic of organized complexity – the characteristic heidentified as ‘‘wholeness.’’A New Theory of Urban Design is not among Alexander’s best-known works. It is



surely eclipsed by such familiar works as his landmark PhD thesis, which became hisfirstbook, Notes on the Synthesis of Form (1964); his elegant little paper on differentialurbangeometry, ‘‘A city is not a tree’’ (1965); his perennial bestseller A Pattern Language(Alexander et al. 1977), reportedly the best-selling treatise on architecture of all

time; andits companion volume, The TimelessWay of Building (1979). According to HarvardDesignReview Editor William Saunders, A Pattern Language ‘‘could very well be the mostreadarchitectural treatise of all time’’ (Saunders 2002). By comparison, A New Theory wasamodest seller, and did not seem to have anything like the professional impact of theothers.

Yet two decades later, the little volume seems to carry an influence far beyond itsinitialsales would suggest. We hear its ideas still discussed today, 5 and we may find itsittingprominently on rather unlikely bookshelves.Moreover, as argued herein, it serves asa kind of milestone in the discourse on process and generativity in urban design.Even Alexander’s own assessment would not suggest that A New Theory should havethe legacy it has. Alexander himself argued later that the book’s focus was still tooheavilyupon the formal design product, and did not deal sufficiently with processes of socialinteraction, site assessment, financial arrangements, or construction sequencing andmanagement. Even the basic problem of geometric form was not dealt withsufficiently, heargued. All these topics would be taken up in far greater detail in his much morerecentmagnum opus, The Nature of Order (2003–04).

Yet in this volume, Alexander and colleagues did squarely reintroduce the notion of process into the debate about urban design – a process that aims, above all, togeneratewholeness within the urban structure:We have therefore used the phrase urban design in the title of this book, since it seems to usthat urban design, of all existing disciplines, is the one which comes closest to acceptingresponsibility for the city’s wholeness. (Alexander et al. 2003–04, p. 3)But Alexander wants to challenge the very notion of design, and its sovereignty overcitymakingas a technical exercise or a creation of ‘‘master plans:’’But we propose a discipline of urban design which is different, entirely, from the one knowntoday. We believe that the task of creating wholeness in the city can only be dealt with as aprocess. It cannot be solved by design alone, but only when the process by which the city getsits form is fundamentally changed. (Alexander et al. 2003–04, p. 3)

The echoes of Jacobs are readily recognizable. But there are also echoes of Alexander’sown earlier work on the overlapping networks within cities, discussed in ‘‘A city is notatree’’ (Alexander 1965). There are echoes of the earlier preoccupation with theproblem of morphogenesis, the synthesis of form, and in particular the mereological relation of partsand wholes, that has been Alexander’s focus from the beginning of his career to thisday.



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The significance of A New Theory of Urban Design may be that it did, tentatively,proposea specific process by which a group of collaborators on an urban project might createsuchorganic wholes more successfully, following a series of explicit rules.In the experiment that forms the second section of the book, Alexander had 18graduate students play various roles in a simulated process of urban growth. Therolesincluded designers, developers, citizens, administrators, and others, making up apopulation not unlike that involved in the growth of a historic small city, or thecommunity-led development of an actual neighborhood.

The role-players followed one overriding rule: every increment of construction mustbemade in such a way as to heal the city. Here he uses the word ‘‘heal’’ in the originalsenseof ‘‘to make whole.’’ That is, we must take a series of incremental steps inconstruction,and at each step we must make an assessment about whether the proposedconstructionadds to, or takes away from, the wholeness of the city.He further defines this rule as follows: every act of construction has just one basicobligation: it must create a continuous structure of wholes around itself. That is, wemust look at the way that the construction forms and changes patterns, and whetherthose patterns are patterns of coherent wholes, or of poorly related fragments andslivers. An extreme example of the latter is what planners derisively call ‘‘SLOAP’’ –‘‘space left over after planning.’’ An example of the former is a nicely formed newspotthat we would find appealing to be in, and that we would find well related to thespacesaround it.How are these wholes to be understood and manipulated? Alexander, ever the

Cambridge mathematician, introduces a geometric entity he calls a ‘‘center’’ – a keyelementof the theory explained in more detail in his later and much larger work, The Natureof Order(2003–04). Philosophers of process will recognize strong similarities to Alfred NorthWhitehead’s system of ‘‘actual entities’’ in that philosopher’s magnum opus, ProcessandReality (1928). But in essence, centers are simply localities, or ‘‘spots,’’ embeddedwithin afield of other centers. A center is not a ‘‘point,’’ but rather, a field – as Alexander putsit, ‘‘awhole, made of subsidiary wholes.’’A field of centers, then, is a nested series of localities that frame one another and

variously connect to one another in a pattern of relationships. Such a field comprisesitsown center at a larger scale. Conversely, every such center is embedded in a field of othercenters that affect its structure and the structure of the wholes that result from theircombinations. This field is contextual and infinite, but the contextual influence of moreremote centers will generally recede with distance.So too, every center incorporates other centers at smaller and smaller scales:houses,



rooms, corners, floor tiles, patterns, etc. However, these smaller centers need not allfit neatlywithin the larger center: they can overlap with other larger centers as well.

The usefulness of this approach can be understood in a series of examples. The cathedral design in Figure 3 can be seen as a relatively simple series of geometrically related centers. Every part of the structure feels coherent and well

related tothe other parts. Every region sits neatly nested within larger regions, with someoccasionaloverlap, while every region is simultaneously composed of smaller regions. At thescale of a building, the plan feels whole and appealing. If it were a larger structure – if it weretheplan for a city, for example – it might feel much too rigid and imposed.Figure 4 shows a much more complex series of centers from Giambattista Nolli’sengraved plan of Rome (1748). Highlighted are only a small number of them toillustratethe point. Note again that at the scale of buildings the centers are fairly neat andsymmetrical. At larger scales, the centers tend to overlap and wend around oneanother,forming much more ‘‘organic’’ patterns. As Jacobs described, the ‘‘organic’’ characterof


these patterns is nothing other than the complex set of relationships by which theyare‘‘interrelated into an organic whole.’’Figure 5 shows an obvious counter-example. The large, undifferentiated geometrymakes no attempt to adjust itself to its surrounding space. The shape of the paving,fencing, and other elements bears strikingly little relation to the space around them,andthe overall form is unappealing in the extreme. This is a good example of the kind of outdoor space that planners derisively refer to as ‘‘SLOAP.’’

The structuring process the students followed is as follows.As one center ‘X’ is produced, so, simultaneously, other centers must also beproduced, at three well-defined levels:Larger than X. At least one other center must be produced at a scale larger than X, and in sucha way that X is part of this larger center, and helps to support it.

The same size as X. Other centers must be produced at he same size as X, and adjacent to X,sothat there is no ‘‘negative space’’ [i.e. SLOAP] left near X.Smaller than X. Still other centers must be produced at a scale smaller than X, and in such away that they help to support the existence of X.Alexander and his students structure the centers of their projects with seven‘‘detailed rulesof growth.’’ Each of these is composed of still other sub-rules:

NPiecemeal growth governs the increment of growth, the distribution of elements,

andthe diversity of uses.

N The growth of larger wholes governs the way that emergent wholes are identifiedandreinforced, so that they become large-scale features of the urban plan. In this way,Figure 4. Giambattista Nolli’s engraved plan of Rome; a detail from his Nuova pin˜ata di Roma(1748). Note the much more complex system of messy, overlapping regions and centers.64 M.W. MehaffyDownloaded At: 18:28 21 April 2011



such large-scale features as main streets, public squares and the like emerge fromthesequential process, not unlike the way they did in many historic cities.

N Visions ensure that the human participants will use their perceptual andimaginativeability at each step to assess the coherence of each increment. This is necessary toensure that each increment is a well-adapted human space, with attributes of mostvalue to human beings.

N Positive urban space ensures that there is no SLOAP around the structures, andthatpedestrian space, gardens, streets, and other exterior spaces are well formed andcoherent.

N The layout of large buildings provides detailed steps for the successful layout of area,size, entrance, main outdoor elements, major interior areas, and so on, for eachlarge building. This section of the process comes very close to what Alexander latercame to call a ‘‘generative code’’ (see below).

N Construction deals with the details of a building, and the iteration between how itisto be built and how it is to appear.

N Formation of centers provides detailed guidance of the geometric shaping of centers,as a kind of tension between its own internal tendency to create local symmetry, andthe larger adaptation that tends to pull the symmetry apart. For Alexander thegeometer, this is a characteristic feature of whole systems:One of the reasons we can always recognize a real structure of centers as fast as wedo isthat we can always detect the truth in the balance of symmetry and asymmetry,even whenwe do not know what is going on functionally:

Thus, we may see the creation of the field of centers, as the creation of a loosely connectedsystem of local symmetries, always relaxed, always allowing necessity to guide it, in such awayas to produce the deepest possible structure of centers, at every scale. (Alexander et al. 2003–04,p. 95)

Thus, Alexander’s approach is fundamentally contextual, relying upon a continuouscyclical, stepwise response to existing conditions. In actual projects, Alexander oftenasksparticipants to walk the site, set stakes, meet residents, spend time, and let the site’sFigure 5. An example of ‘‘space left over after planning’’ (‘‘SLOAP’’). This is residual space withapurely accidental and fragmentary structure of centers. Not surprisingly, as urban space itoften

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attributes seep in (see Figures 6–9). He often continues this process through thedesign andthe construction, even into the maintenance and repair of a completed project. In thisexercise, Alexander and his students used a large-scale model as an approximationof theactual site. They did visit the actual site, and incorporated a number of its existingstructures into the model at the outset.



Alexander’s challengeA New Theory of Urban Design amounted to a gauntlet thrown down to conventionalurban design, not unlike that thrown down by Jacobs 26 years earlier.Alexander himself was tentative about the particular methodology he proposed.Indeed, as discussed, he later offered his own critique of its shortcomings. But he wasnot

then, nor has he been since, tentative about the key theoretical points on which thismethodology differed from conventional practice:

N Urban design must not be an act of tabula rasa imposition of a form designedremotely, based upon an abstract program. It must understand, respect, and seek toimprove the existing conditions.

N Urban design must incorporate the decisions and needs of the local stakeholders,asa matter not only of fairness, but also of the intrinsic quality of the result.Figures 6–9. Alexander’s generativity from natural and cultural sources can be seen in theexampleshere. Figure 6 (top left), the cultural expression of a Japanese school; and, Figure 7 (top right),aCalifornia farmer’s market. Figure 8 (bottom left), a generative process to stake out a new

neighborhood in Colombia; and, Figure 9 (bottom right), a drawing of such a community after ithasbeen staked on site.66 M.W. MehaffyDownloaded At: 18:28 21 April 2011

N Above all, urban design must be a generative process, from which a form willemerge– one that cannot be pre-planned or standardized, but will of necessity be, at least insome key respects, local and unique.Implementation: the ‘‘many hands’’ of the New UrbanismPerhaps the most notable example of an effort to implement Alexander’s ideas – and

Jacobs’s in equal measure, it should be added – has been the New Urbanismmovement.

The Congress for the New Urbanism was formed by six architects, growing out of a1991workshop at the Ahwahnee Lodge in California’s Yosemite Park. It was ratherironicallymodeled on the Congres International d’Architecture Moderne (CIAM), the highlyeffective organization that propagated the modernist movement in architecture,whichaccelerated the kind of segregation and top-down formalism in city-planning thatboth

Jacobs and Alexander decried.By contrast, the New Urbanism is explicitly about mixed use, and, its proponentswould argue, about process.By all accounts, Andres Duany has played a leading role in the creation of NewUrbanism. His plan for Seaside, Florida, attracted enormous attention and promptedthe coining of the term ‘‘new urbanism’’ by author Peter Katz (with Duany’sencouragement). Duany credits Alexander as being a major influence on the NewUrbanism, and has gone so far as to tell this author that Alexander’s ideas are thebasisof ‘‘everything that we’re doing now’’ (Mehaffy 2004b). The New Urbanism includes aCharter with 27 principles for the structuring of urban form, including emphasis onmixed use, socio-economic diversity, historic preservation, walkability, and relatedobjectives. It also includes a set of methodologies for the urban design process, atthe



heart of which is a workshop tool called a charrette.Named after the cart that once gathered student drawings at the famous Ecole deBeaux-Arts in Paris, the charrette is an intensive design workshop that typically runsfromfour to nine days. It brings together urban designers, transportation planners, civilengineers, government officials, local residents, and other stakeholders and technical

experts as the project may require. The Jacobsian and Alexandrian aim is to focuscollaboration on design, and to produce an emergent result.It is important to understand that a charrette is not merely a ‘‘user consultation,’’ of thesort that was commonplace before The New Urbanism, but a real-time design processinwhich users provide collaborative input, along with an interdisciplinary mix of professionals.It is, according to Duany, an exercise to provide exactly the kind of collaborativesynthesisthat Alexander described in A New Theory of Urban Design.Alexander’s critiqueFor Alexander, however, the charrette is a laudable effort at reform that is stillwoefullyinadequate for the challenge. His criticism rests on three principal objections:

N The charrette process is still a relatively brief and isolated act of master planningdone in a remote room, away from the site, and away from the opportunities andconstraints that might turn up in a longer and more direct process of contextualengagement.

N The participants, especially the local residents, are forced to play a highlycircumscribed role, in which the ‘‘outside experts’’ disproportionately influence theprocess.


N The master plan is then usually turned over to a developer, who can theninterpretthe master plan in a variety of usually disastrous ways. Most importantly forAlexander, the developer typically builds structures that are not at all generative,but based upon standardized templates, with the result that they feel lifeless andunsuccessful. They may have the outward appearance of a more organicneighborhood, but they are, in the end, standardized reproductions.For Alexander, the most serious problem is the fact that the output of the charrette –a‘‘master plan’’ – is usually turned over to developers:I think that many of the people who are involved in the CNU actually have not understood theproblems that the developer represents, and what has got to be done in order to change thatsituation. It’s very very serious. (Mehaffy 2004a)Alexander clearly feels great sympathy with the New Urbanists, but equally clearlyfeelsunease at the result of New Urbanist work:I’m proud of them, because they’ve really done something to help change things. But whenyou say, well, what are the rules that they actually live by? I’m talking about ‘‘live by’’ whenthey’re shaping something, modeling it, drawing it, planning it, things like that – building it,and so forth – the concepts that they are living by there are not those which I’ve just beenspeaking about, having to do with whether you’re making part of nature. They’re actuallysomething highly artificial …. (Mehaffy 2004a)

The New Urbanists’ rebuttal – and a counter-critiqueFor New Urbanists such as Duany, Alexander’s critique misses a key point. Yes, thereare



standardized templates within The New Urbanism – as, for example, the so-called‘‘parti,’’a basic plan drawing of the scheme. But that structure can then be adapted andallowed toserve as a skeletal form for more organic growth. In effect, it can serve as a kind of welldesigned

‘‘trellis’’ on which organic growth can self-organize. Duany notes that suchcombinations of the standard and the contextual are common in nature.Duany and others point to Alexander’s own patterns as typological structures thatare,in part, standardized elements within his own design system (though a networkedone, andnot a strict hierarchy). They are then adapted to the specific context, and used in akind of flexible grammar. Duany believes he is doing something very similar (and indeed,oftenusing Alexander’s own patterns). ‘‘I am the best Alexandrian,’’ he recently told theauthor.Moreover, Duany believes Alexander is failing to come to terms with a core reality of modern technological society: 6 that large numbers demand top-down managementmethods. In a mass society, the norm quickly reverts to chaos and kitsch. In order toimplement Alexander’s methods, this demands expert, top-down leaders for thedesign andconstruction process – a role, Duany points out, that Alexander himself often plays inhisown projects. But the scale of reform does not permit the kind of painstaking one-off approach for which Alexander is known.

These points were evident in comments by Duany in an interview with the author(Mehaffy 2004b). He was asked to expand on his comment that ‘‘getting thingsimplementedon a large scale’’ was one of the aspects of modernity that interested him:Isn’t there a danger, as Chris Alexander has warned, that that kind of large scale doesn’t allowthe grain of adaptation that’s going to be required for good urbanism and good architecture?Isn’t scale one of the key things that the modernists screwed up on so badly?Duany replied:

Yes scale is a prime problem, but it is also THE reality of modernity. It cannot be avoided. Ibelieve it was Giedion, the theoretician of modernist architecture who said: ‘‘Ours is theproblem68 M.W. MehaffyDownloaded At: 18:28 21 April 2011

of large numbers’’. These earlymodernists were very smart. There is immense populationgrowth,even in the U.S.; there is the blinding speed of communication, of automatic decision protocolsand of mass production. If we return only to the crafting of cities, what we do may be of highquality but it will not be important. (Mehaffy 2004b)For Duany and other critics, Alexander’s proposal is to return to a painstaking one-off process of organic design, which is simply not up to the scale of the present

challenge.Rather, we must create more automatic processes that generate the same result, notunlikeseeds that generate vast numbers of living structures:… What we must craft now are not the communities, but the programs that create themquickly automatically, replicating the organic process of sequential decisions. This mustachieve the authentic variety and resilience of traditional communities. These protocols mustbe propelled by the power grids, and not be tied to the limits of our personal efforts. Every oneof our ‘‘adversaries’’ operates from automated protocols. Protocols that flow 200 mortgagesfor 200 parametric strip shopping centers, all bundled for purchase in a single transaction by



an insurance company. What would they do with our one-off creations? Inspect themindividually? They can’t. (Mehaffy 2004b)

The reference to ‘‘power grids’’ echoes a discussion that Duany and Alexander had in1988. According to Duany, Alexander said to him, ‘‘we both know what the applianceis.What we need to do now is to design the plugs to connect to the current power grid’’(Mehaffy 2004b). For Duany, Alexander has neglected this task, whereas the NewUrbanists have pursued it with full force – accounting for the latter’s much moreprodigious output of projects.So Duany and other New Urbanists have turned to a new project: the development of codes that replace the old, destructive protocols with new ones that allow goodurbanismto flourish, as if on well-constructed trellises. The ‘‘SmartCode’’ is a form-based codethatreplaces the segregated ‘‘Euclidean’’ zoning of an earlier era with a series of parametricspecifications designed to ensure coherent streetscapes and public realms. The codeuses a‘‘transect’’ system to organize contextual responses to the urban condition, from themostintense urban setting to the most pristine natural environment.Alexander’s ‘‘generative’’ codeBut for Alexander, again, this kind of code does not address the core prerequisite of generativity, and without such guidance for growth the result is still likely to bewellaligned,lifeless junk. It prescribes a series of static parameters within which generativeevents may occur, but it does not in any way facilitate or guide theirgeneration.Moreover,even to specify such parameters is to constrain the emergence of organic wholes,whichrequire an environment in which adaptation of form can occur as needed.Almost in response to the New Urbanists, it would seem, Alexander has proposed analternate kind of code, based explicitly upon rule-based, generative processes of thekindoutlined in A New Theory of Urban Design. Alexander’s ‘‘generative code’’ addressesnotphysical parameters of the built environment, but steps that the participants shouldtaketogether in laying out and detailing a given structure. Alexander likens it to a recipe,or amedical procedure, in which the steps always follow a logically similar pattern, buttheactual actions continuously adapt to the context – the taste and texture of the food inthecase of a recipe, or the condition of the patient’s tissues in a medical procedure. Butin thiscase, the ‘‘recipe’’ or the ‘‘procedure’’ guides the unfolding of environmental form.In its fullest form, this kind of generative code can be thought of as a design–buildsystem, addressing all of the conditions of building – financing, ownership,management,sourcing, and, crucially, changes to the design along the way. For Alexander, theissue of cost control is a manageable process, and indeed, is done regularly within existingdesign–




build approaches. He points out that much of the direction of technology is todayaimedfavorably for such an approach – one-off manufacturing, customization, nichemarketing,and so on. He is convinced of the possibility and even the inevitability of thistransformation of technology, in a more adaptive, ultimately organic direction.

Nonetheless, Alexander recognizes that there are enormous challenges ahead tomaking a practical version of such a system. He continues to work with a growinggroupof collaborators (including the author) on such a project, and he has repeatedlystated thathe welcomes the opportunity to develop collaborations with New Urbanists likeDuany, aswell as others.Alternative approaches to generativityDuany’s discussion of the ‘‘problem of large numbers’’ would find a sympatheticaudiencewith the architect and theorist Rem Koolhaas, his forensic opponent in a ratherlacklusterdebate in 1999 at Harvard’s Graduate School of Design. For Koolhaas – perhapsrepresenting many other contemporary ‘‘neo-modernist’’ architects – the modern cityissimply too complex to yield to a reform agenda like that of the New Urbanists. In thefaceof sheer quantity, architecture is powerless to change the direction of the urbanwave, andtherefore is wiser to seek merely to surf that wave with skill:

This century has been a losing battle with the issue of quantity. …In spite of its early promise,its frequent bravery, urbanism has been unable to invent and implement at the scaledemandedby its apocalyptic demographics. (Koolhaas 1995)Koolhaas challenges Duany’s faith in planning, and suggests that urbanism is nowthe art

of accommodating generativity, rather than the futile attempt to ‘‘design’’ it:If there is to be a ‘‘new urbanism’’ it will not be based on the twin fantasies of order andomnipotence; it will be the staging of uncertainty; it will no longer be concerned with thearrangement of more or less permanent objects but with the irrigation of territories withpotential; it will no longer aimfor stable configurations but for the creation of enabling fieldsthataccommodate processes that refuse to be crystallized into definitive form …. (Koolhaas 1995)Another approach to generativity is typified by Peter Eisenman, Alexander’s partnerin afamous and telling debate in 1982, since billed as ‘‘Contrasting Concepts of HarmonyinArchitecture’’ (Eisenman and Alexander 1982). In his book Code X: The City of Culture of Galicia (Eisenman Architects 2005), Eisenman discusses his theory of coding as agenerative method of producing form. The theory was put to the test in the City of Cultureof Galicia project in Santiago de Compostela, Spain, the most urban in scale of Eisenman’s projects (see Figures 10–13).

The project narrative describes a transition from an architecture of semiotics(symbolicexpressions) to an architecture of generated geometries or ‘‘traces:’’

This post-semiotic sensibility is not dominated by easily consumed imagery of signs andsignifieds, but rather is understood as a series of traces, marks that produce an alternative



condition of figure and ground. The City of Culture evolves from the superposition of threesets of traces. First, the plan of the medieval center of Santiago is placed on the hillside site,which overlooks the city. Second, a Cartesian grid is laid over these medieval routes. Third, thetopography of the hillside is allowed to distort the two flat geometries, thus generating atopological surface that superposes old and new in a simultaneous matrix.

The original center of Santiago conforms to a figure/ground urbanism. The buildings are figuraland the streets, residual. Through this transformative mapping operation, our project emerges

asa warped surface that is neither figure nor ground but both a figured ground and a figuredfigurethat supercedes the figure-ground urbanism of the old city. Santiago’s medieval past appearsnotas a form of representational nostalgia but as an active present found in a tactile, pulsatingnewform. (Eisenman Associates 2007)70 M.W. MehaffyDownloaded At: 18:28 21 April 2011

The generativity in Eisenman’s approach can be contrasted with the generativityexhibitedin the nearby historic town it echoes (Figure 10). The latter has emerged from thecollaborative and rule-based actions of many actors over time, and from the

environmental conditions to which they have adapted. Artistic abstractions andplanningschemata do occur, but are expressed as local elements within the more globaladaptationsto environment, culture, human activity and need.By contrast, Eisenman’s generativity is used solely as a resource for one artist’sexpressive master plan, imposed on the site at a very large scale. In that sense itssemioticsis in fact alive and well, but disguised within a subtler artistic reference to incidentallygenerated traces of its natural subject. It regenerates only the most skeletallyabstractaspects of the historic evolutionary pattern, so as to avoid ‘‘representationalnostalgia.’’ Itis otherwise a static and non-adaptive work of art.Koolhaas’s and Eisenman’s positions here can be contrasted with Jacobs’s. 7 For

Jacobs, urban practice was a proper intervention in the interest of the health of anurbansystem, accomplished by patient inductive study and by manipulation of subtlecatalyticfactors. Art was a dimension of this work, but far from its only dimension. She wouldarguably regard Koolhaas’s nihilism as little more than the predictably frustratedreactionto a continued failure to adopt the most recent and most accurate model of ‘‘the kindof problem a city is.’’ She would arguably regard Eisenman’s position as an altogetherdifferent model – a hijacking of the city by fine artists, who would see it transformedintoan enormous abstract sculpture gallery. This, she frequently warned, was adangerousattitude: ‘‘The city cannot be a work of art’’ (Jacobs 1961, p. 372).Figures 10–13. Figure 10 (top left), the relation of the plan to the organic terrain and medievalcity;and, Figure 11 (top right), the conceptual diagram of the plan. Figure 12 (bottom left), a sitemodel;and, Figure 13 (bottom right), the project under construction. Courtesy: Eisenman Architects.




Interestingly, both Koolhaas and Eisenman have recently expressed remarkablypointed misgivings about the efficacy of their approach, and the larger artistic cultureof which it is part. Speaking in Montreal in June 2007, Koolhaas lamented the effect of laissez-faire market forces on the profession:If you look back over the past 2,000 years, architecture dignified civic and public life. Then themarket economy happened, replacing all former values and erasing almost all ideology overthe entire world. What it represents for all of us today is an invitation to simply be extravagantand spectacular. … The work we do is no longer mutually reinforcing, but I would say thatany accumulation is counterproductive, to the point that each new addition reduces the sum’svalue. … So there are many problems, first of all our work, which is not able to find its wayout of this recurring dilemma, then there are the many reasons to question our sincerity andmotives. (quoted in La Giorgia 2007)Eisenman, speaking at the same event, argued that we are in the late period of modernism– its ‘‘death rattle’’ – but we are struggling to find a new paradigm to replace it:We are in the rococo phase of modern architecture. … The problem we need to solve is theurgency of media to have something new to look at and talk about all the time. Our need to bein the news all the time. … The slowness required to find and understand meaning inarchitecture no longer has any attraction. [We need an architecture] that asks how, at thismoment in time, without a new paradigm, can we understand our discipline and our culture ina different way. (quoted in La Giorgia 2007)Or perhaps we need to look more deeply for a new paradigm within the insights of modernscience and philosophy. This is precisely what Alexander has said he is seeking. 8

In the planning disciplines, generativity has continued to develop in the work of otherinvestigators. In particular, the trend toward engagement of residents evident in the‘‘thirdgeneration’’ of the design methods movement has continued and accelerated. Anotableexample is so-called Communicative Planning, which seeks to build inclusiveness,incorporate difference, reach out to marginalized groups, and sensitize planners to awide variety of viewpoints and alternative ways of knowing (Qadeer 1997,Sandercock

2000, Harwood 2005). Sandercock (1998) describes the evolution of a ‘‘utopia with adifference’’ (pp. 5, 119) a similar concept to Friedmann’s (2002) ‘‘open city’’ of diversepeoples, united by applied principles of ecology, citizenship, and regionalgovernance. Theplanning profession has been plagued by the lack of a workable knowledge baseabouthow to communicate with diverse population groups (Wallace and Milroy 1999), butwenow see how ‘‘a thousand tiny empowerments’’ can help to constitute a moresociallytransformative planning process (Sandercock 2000).Communicative planning seeks to achieve collaborative consensus-building by, in

effect,developing ‘‘‘conversations’ between stakeholders from different social worlds’’(Healey1997, p. 219). Innovation, ‘‘drama,’’ and ‘‘a sense of play’’ are ways to ‘‘move theplayers andembed their learning deeply’’ (Innes and Booher 1999, p. 19).ConclusionFor all their disagreements, the cross-fertilizations between Alexander’s processadvocatesand the New Urbanists continue, with constructive results. The topic of generativity



continues to loom large. 9 Duany’s SmartCode – now adopted by dozens of municipalitiesand under consideration as the national planning code of Scotland, among others –hasbegun to take on some stepwise layout guides very similar to Alexander’s. (SomeAlexander

allies, including this author, continue to urge the expansion of this offering.) Duanyarguesthat his code also incorporates many other aspects of generativity. For his part,Alexanderhas continued to develop his proposal for a ‘‘generative code,’’ and to address the‘‘massive72 M.W. MehaffyDownloaded At: 18:28 21 April 2011

process difficulties’’ that are posed by conventional building protocols, using many of theNew Urbanists’ insights. 10

To be sure, Alexander faces daunting challenges that the more pragmatic NewUrbanists seem uniquely positioned to help meet. In fact, each seems to have acomplementary grasp on aspects of the problem that the other, through area of focusorthrough sheer personality, seems much less able to address. This emerging model of collaboration may hold more promise than either may realize.A growing group of collaborators has assembled around this sharable,complementaryagenda, and begun to pursue lines that Alexander (for one) does not seem to find asinteresting – most significantly, ‘‘open-source’’ collaborations with biologists,ecologists,sociologists, computer scientists and others. Such ‘‘open source’’ methods haveyieldedremarkable results for the computer software developers who exported Alexander’sideasinto that realm with remarkable effect. 11

In an age of critical ecological and economic challenges, in which human technologyseems at nearly irreconcilable odds with ecological sustainability, Alexander arguesthat wemust have a much more serious look at the way that natural systems use generativeprocessesto achieve sustainable morphologies, and work to integrate those lessons into ourownhuman systems. 12 Though progress has been slow – and yet, as has been arguedherein,substantial – Jacobs and Alexander demonstrate that this is a comprehensibleproblem, andnot one that is (to quote from Jacobs’s caricature, paraphrasing Warren Weaver) ‘‘insome

dark and foreboding way, irrational.’’ The opportunity remains to develop furthergenerative processes as a means to deliver more robust and more efficacious results– that is,more sustainable results – within the field of urban design. But that task will surelydemandthe combined and synergetic efforts of Alexander, Duany, and many others.Notes1. A ‘‘design parti’’ was a schematic diagram used early in the Beaux-Arts design process.‘‘Parti’’means to divide, hence to organize basic regions of the plan schematically in a diagrammatic



scheme.2. Note, however, that Alexander does use master plan drawings as a form of designcommunication, or entitlement documentation. He is, however, careful to emphasize that theyare snapshots in a longer process, and not any sort of ‘‘final’’ result. He does so by includingexplicit generative processes as part of the planning documents. See, for example, The MasterPlan and Process for Harbor Peak (Alexander 2006: http://www.livingneighborhoods.org/library/brook-1.pdf).

3. Several correspondents have related discussions with Jacobs along these lines. The author isparticularly indebted to Arun Jain, Chief Urban Designer for the City of Portland, whodiscussed these matters with Jacobs on a number of occasions.4. Reported in a seminar discussion at University College London, where the author waspresent.5. Most recently, the author spotted a well-thumbed copy sitting conspicuously on the shelf of theExecutive Director of a major New Orleans preservation charity. As it was pointed out to her,she remarked, ‘‘Oh, yes – I love that book!’’6. The author is indebted to Andres Duany for a number of conversations on this topic. Anyerrorsin representing his views are entirely the author’s own, for which apologies are given inadvance.See in particular his interview in Mehaffy (2004b).7. At any rate, Jacobs did seem to regard the urban interventions of Koolhaas’scontemporaries,including Eisenman, with dismay. In a letter to the author in 2001, she related that she was‘‘appalled’’ at the proposals for Ground Zero in New York. She only refrained from gettinginvolved, she said, because she was no longer a New Yorker. But she referred the author toothercolleagues in New York who were said to be preparing to oppose the plans.


8. There is an extensive discussion of this topic in Grabow (1983). Alexander also discussedthistopic in the present author’s interview with him (Mehaffy 2004a, 2007).9. Indeed, even at the time of writing, it is the subject of a very animated exchange on a NewUrbanist listserv, including Duany, his colleague Sandy Sorlien, the present author, and others.10. At the Congress for the New Urbanism in 2006, Alexander held a meeting at which some30people, including a number of prominent developers, pledged to collaborate with him. Alistservwas formed, and plans were made for a symposium – which was put on hold when Alexanderwas unable to finalize an agreement with the Prince’s Foundation for the Built Environment tohost it.11. See, for example, the explosive growth of the ‘‘design pattern’’ movement in software,based on APattern Language, and begun by former Tektronix engineers Ward Cunningham and Kent Beck.Alexander’s ideas have thus directly spawned the development of such familiar titles asWikipediaand The Sims. Cunningham has been involved in the more recent collaborations to developAlexander’s ideas on generativity further.12. For example, very promising and hopeful work is being done within game theory andeconomics, notably in the realm that seeks to integrate so-called ‘‘externalities’’ within more

sustainable economic processes. This echoes Alexander’s efforts to ‘‘change the rules of thegame’’ of real estate development.ReferencesAlexander, C., 1964. Notes on the synthesis of form. Cambridge, MA: Harvard University Press.Alexander, C., 1965. A city is not a tree [2 parts]. Architectural Forum, 122 (1), 58–62 (Part I);122 (2), 58–62 (Part II). Available from: http://www.arq.ufmg.br/rcesar/alex/alexander/alexander1.html/.Alexander, C., 1979. The timeless way of building. New York, NY: Oxford University Press.Alexander, C., 2003–04. The nature of order, Books 1–4. Berkeley, CA: Center forEnvironmental

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NY: Oxford University Press.Batty, M., 1991. Cities and fractals: simulating growth and form. New York, NY: Springer.Batty, M., Couclelis, M. and Eichen, M., 1997. Urban systems as cellular automata. London(UK):Pion.Broadbent, G., 1979. The development of design methods a review. Design Methods and

Theories, 13(1), 41–45.Dulgeroglu-Vuksel, Y., 1999. Design methods theory and its implementation for architecturalstudies. Design Method: Theories, Research, Education and Practice, 33 (3), 2870–2877.Eisenman Architects with Davidson, C.., ed., 2005. Code X: the city of culture of Galicia. New

York,NY: Monacelli.Eisenman Associates, 2007. Narrative for design of City of Culture, Santiago de Compostela,Spain[online]. Columbia University Graduate School of Architecture, Planning and Preservation.Available from: http://www.arch.columbia.edu/index.php?pageData532552/ .Eisenman, P. and Alexander, C., 1982. Contrasting views of harmony in architecture. Transcriptof adebate at Harvard Graduate School of Design [online]. Katarxis 3, Available from:www.katarxis3.com/ .Fowles, B., 1977. What happened to design methods in architectural education? DesignMethods and

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Grabow, S., 1983. Christopher Alexander: the search for a new paradigm in architecture.Boston, MA:Oriel.Harwood, S.A., 2005. Struggling to embrace difference in land-use decision making inmulticulturalcommunities. Planning, Practice and Research, 20 (4), 355–371.Healey, P., 1997. Collaborative planning – shaping places in fragmented societies. London (UK):Macmillan.Hillier, B., 1989. The social logic of space. London (UK): Cambridge University Press.Hillier, B., 1999. Space is the machine: a configurational theory of architecture. London (UK):Cambridge University Press.Innes, J.E. and Booher, D.E., 1999. Consensus building as role playing and bricolage: toward atheory of collaborative planning. Journal of the American Planning Association, 65 (1), 9–26.

Jacobs, J., 1961. The death and life of great American cities. New York, NY: Vintage.Koolhaas, R., 1995. Whatever happened to urbanism. In:Koolhaas, R. S, M, L, XL. New York, NY:

Monacelli, 958–971.La Giorgia, G., 2007. Market v. meaning. Architecture Week, 5 September [online]. Availablefrom:http://www.architectureweek.com/2007/0905/design_3-1.html/ .Mehaffy, M., 2004a. A conversation with Christopher Alexander. Katarxis 3. Available from:www.katarxis3.com/ .Mehaffy, M., 2004b. An interview with Andres Duany. Katarxis 3. Available from:www.katarxis3.com/ .Mehaffy, M., 2007. On the nature of order: an interview with Christopher Alexander. UrbanDesign

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International, 12, 51–57.Qadeer, M.A., 1997. Pluralistic planning for multicultural cities: the Canadian practice. Journalof the American Planning Association, 63 (4), 481–494.Sandercock, L., 1998. Towards cosmopolis. Chichester (UK): Wiley.Sandercock, L., 2000. Cities of (in)difference and the challenge for planning. Dokumente undInformationen zur Schweizerischen Orts-Regional und Landesplanung (DISP), 140, 7–15.

Saunders, W., 2002. Book Review: A Pattern Language. Architectural Record, May, 93.Availablefrom: http://www.gsd.harvard.edu/research/publications/hdm/back/16books_saunders.html/ .Simon, H., 1962. The architecture of complexity. Proceedings of the American PhilosophicalAssociation, 106, 467–482.Wallace, M. and Milroy, B., 1999. Intersecting claims: planning in Canada’s cities. In: T. Fenster,ed.Gender, planning and human rights. London (UK): Routledge, 55–73.Whitehead, A.N., 1928. Process and reality. New York, NY: Free Press.


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