aspects of urban form

Urban Morphology (2009) 13 (2), 105-20 International Seminar on Urban Form, 2009 ISSN 1027-4278

Aspects of urban form

Karl KropfUrban Morphology Research Group, University of Birmingham and

Roger Evans Associates Ltd, 59-63 High Street, Kidlington, OX5 2DN, UK.E-mail: [email protected]

Revised version received 23 March 2009

Abstract. The diversity and complexity of human settlements is reflected in therange of ways we try to understand them. The richness of subject matterpresented by cities has given rise to an equal richness in methods ofinvestigation. Even within a single field such as urban morphology, there aredifferent approaches with different terms of reference. The challenge raisedby the diversity is not how to select between the different views but how tocombine and co-ordinate them. The purpose of this paper is to undertake aninitial critical analysis of different approaches to urban morphology in aneffort to meet that challenge. The first aim is to identify the range of differentphenomena taken as the object of urban morphological enquiry. The secondis to identify an aspect that is common to all the approaches and that can beused as a reference key to co-ordinate different views in a rigorous way. Theultimate goal is a composite view in which the different approaches supporteach other to provide a better understanding of human settlements.

Key Words: urban form, spatial analysis, space syntax, process typology,historico-geographical approach

It might be said that the gamut of humancivilization is condensed within the urban.Villages, towns and cities present a density andrichness of subjects that is hard to find in anyother human product. That richness is evidentnot only in the wide diversity of settlementsand the depth of their complexity but also interms of our capacity to identify and selectdifferent aspects to explain.

Just as settlements are diverse and complex,so there are many ways to describe andunderstand them. To only touch the surface,approaches range across the broad categoriesof social, economic and environmental andfocus variously on the statistical, spatial/geographical, formal, historical, psychological,informational and aesthetic dimensions. Evenwithin a particular area of interest, there are

commonly a number of different approachesfocusing on the same thing.

So, if we acknowledge that humansettlements are diverse and multi-faceted, weshould not be seduced by the superficialattractions of a single point of view. And toacknowledge the wide range of methodsshould not put us on a tower of Babel, deaf tothe voices of others. Rather it should place usat the confluence of routes radiating out to thedifferent regions of the world. This isparticularly true of the morphologicalapproach which, as originally conceived byGoethe, should be an independent study thatmakes use of the findings of all the othersciences, co-ordinating them under theunifying aspect of form (Wilkinson, 1962, pp.177-8).

106 Aspects of urban form

A similar, though slightly stronger, viewcomes from Kevin Lynch (1981, p. 37) wholikens theories of city form to the branches ofa tree, but states that,

unlike the branches of trees we know, theyshould not diverge. They should interconnectand support each other at many points. Acomprehensive theory of cities would be a matof vegetation, and some day the branches willno longer exist in separate form.

Even in seeking the milder connections of co-ordination (as opposed to a comprehensiveunification), the current state of our under-standing would appear to acknowledge thereare a number of unresolved splits or gaps tobridge along the way.

There is the disparity between the fact thatcities are the result of deliberate and co-ordinated human effort on the one hand andexhibit characteristics of self-organizationand emergent behaviour on the other. Cancities be both planned and emergent? If theyare both, what is the balance between the twoand can we articulate the relationship andinteraction in more detail? What is the relationbetween local processes and global structure?

There would also appear to be a parallel splitbetween on the one hand our ability to identifyand describe coherent structures andrelationships and on the other the seeminglyinescapable level of ambiguity that emergesfrom close scrutiny. By what means shouldwe seek to co-ordinate the different views andapproaches?

In a number of fields, evolutionary thinkingseems to be providing a common frameworkwith the most promising potential to bridgethese gaps. Yet again, it is not clear that thereis a common idea of what exactly is evolvingor adapting. Nor is it clear which (or whichcombination) of the related theories ofevolution, developmental biology (morph-ogenesis) or ecology is most appropriate toapply (Kropf, 2001; Steadman, 2008). Thisshould perhaps not be surprising because in aprofound way we are approaching the matterbackwards.

Theories of evolution developed out oflengthy, progressive efforts of classification

and the perception of relationships between thespecies classified. Those theories have beenelaborated and refined over a similarly longperiod of time so that we now have the benefitof ready-made theories that we can try to applyto a range of phenomena. The elaboration ofthe theories has also fed back to ideas aboutclassification, which have been refined in turn.In the case of human settlements, if weacknowledge the complexity, diversity andambiguity of the objects we are seeking tounderstand and the range of different ways wecurrently use to describe them, it is fair to saywe do not have the benefit of a clearly definedset of objects to explain.

The wider state of affairs reflected in thesequestions is represented as a kind of micro-cosm within the field of urban morphology.There are several distinct approaches to thestudy of human settlements that go under thebanner of urban morphology. Close examin-ation of key texts suggests that urban form isdescribed in a number of different ways in thedifferent approaches. The gaps do notrepresent insuperable barriers. Already thedifferent approaches are broadly comple-mentary. How could they be made morerigorously and effectively so?

The purpose of this paper is to explore theseissues through a critical analysis of a few coreconcepts used in the various approaches tourban morphology. The aim is to find aspecific means of co-ordinating the findings ofthe different approaches and help them worktogether and realize the significant potential toestablish a richer multiple description. With aricher and co-ordinated description it mightthen be clearer how the various elements fitinto or inform evolutionary thinking.

Methodology

The goal of the analysis is to identify acommon element, defined in a consistent way,that can be used as a reference key orregistration mark to co-ordinate differentdescriptions. The analysis is not meant as adeconstruction but a sorting through andcomparison of existing concepts and methods.

Aspects of urban form 107

Because the analysis entails a comparison oftexts, it necessarily entails a scrutiny oflanguage and the concepts and phenomena towhich the language refers. That in turnfocuses attention on the particular character-istics of the phenomena that are pertinent tothe authors own objectives (Eco, 1979, pp.77-8, 245-61; Putnam, 1995, pp. 5-26). Theanalysis therefore involves a sorting orclassification of pertinent characteristics intogeneral categories.

This focused analysis is part of a moregeneral process of enquiry that seeks todescribe and explain the phenomena inquestion. Broadly, it is a free movement oriterative cycling through hypothesis, deductionand induction (Peirce, 1958, p. 367). Thestandards for the deductive component of theenquiry are those of formal logic. Ofparticular importance is the distinction madebetween class, relation and property andbetween a class and a member of the class.

For effective comparison, it is necessary toestablish a consistent method of analysis usingthe same set of terms for all examples.Because the common view used in analysis isto see each in terms of classes, relations andproperties, this then provides the best basis forcomparing terms. The question to be asked is,are the terms used in each method defined inthe same way? If not, which offers a betterdefinition? The second question demands avalue judgement. The primary criterion forevaluation is consistency: all instances of agiven definition should be based on the samepertinent characteristics. Secondary criteriainclude specificity definitions should clearlyposit classes of identifiable phenomena insufficient detail; generality definitionsshould be based on pertinent characteristicsfound in as wide a variety of examples aspossible while still allowing for theidentification of specific differences;comprehension definitions should accountfor as wide a range of objects as is appropriateto the task of explanation; coherence definitions should be related to each other in aconsistent way in order to form a clearstructure.

Urban morphology

The obvious and perhaps superficiallybelaboured starting point for critical analysismust be the terms urban morphology andurban form. It is the multitude of assumptionspacked into those terms that is of particularinterest, not at a wider semantic level but interms of the operative definitions manifest inthe works within the field.

While urban by derivation and connotationrefers specifically to cities, the work of urbanmorphologists clearly suggests that the term istaken to refer more broadly to humansettlements. Examples include the studies byConzen (1966) of small market towns andlinear settlements, the works of Slater (1982)on market towns and rural settlements, studiesof suburban development and fringe belts(Stanilov and Scheer, 2004; Whitehand andCarr, 2001; Whitehand and Morton, 2003) andexamination of modern peripheraldevelopment (Levy, 1999) to cite only a few.

Morphology, as originally conceived byGoethe (1952) (see also Wilkinson, 1962) isthe study of physical form, principally ofliving things but also works of art. His majorinsight and contribution was to relate theoutward form of an organism or artisticcreation to its internal structure and to definethe internal parts making up that structure interms of their position relative to each other.Importantly, Goethe also saw outward andinternal form as the product of a process offormation and transformation.

It is worth noting that comparative grossmorphology in plants and animals is one formof evidence that led to theories of evolution.For example, similarity or, more strictly,homology of internal structure such as theskeletal structure of mammals, suggested acommon descent.

While it may again seem laboured, to get atthe use of morphology within the sphere ofhuman settlements, it is worth examining theuse of urban morphology in non-specialistcontexts. Concepts, ideas and theories arefundamentally social and reside, as it were,within a population (Eco, 1979, p. 66; Peirce,


1958, p. 69). Simplified, outdated or partiallycorrect concepts, if commonly held, canpresent an inertial weight or resistance tochange (Dennett, 1995; Gould, 1991, 59-75).

School urban morphology: the persistenceof Burgess and Hoyt

In a number of documents and websitesintended for school level geography (forexample, the General Certificate of SecondaryEducation in the UK), urban morphology isdefined as the pattern of land use within atown (an example in book form is Helm andRobinson, 2002). The models cited are theconcentric zone (Burgess, 1925) and sector(Hoyt, 1939). The material makes reference tobid-rent theory, functional zones, centralbusiness districts and residential zonesdistinguished by income groups. Somesources also distinguish between cities withinMore Economically Developed Countries andLess Economically Developed Countries forpurposes of comparison.

To go beyond the superficial interpretationof land use in this instance, it should beremembered that Burgess was a sociologistand referred to his own work as an ecologicalapproach. With this in mind it is fair to saythat his ideas discerned the relationshipbetween human activities and their urbanenvironment.

In the Dictionary of the social sciencespublished by Oxford University Press(Calhoun, 2002), the focus on land use isshifted and qualified, perhaps as a reflection ofa target audience further through theeducational process. The definition states thaturban morphology

refers to the shape of a city, including itsarchitecture, layout of streets, and differentdensities of habitation. It is often distinguishedin urban studies from functional zonation thepattern of land use in a city.

The examples present two differentconceptions of urban form that eachdistinguish two more or less distinct aspects:physical form and land use or function.

The pragmatic insights of Kevin Lynch

Working within the fields of urban planningand urban design, Kevin Lynch (1981)highlights the lack of clarity in theconsideration of form with respect to use. Heexplicitly defines settlement form as

the spatial arrangement of persons doingthings, the resulting spatial flows of persons,goods and information, and the physicalfeatures which modify space in some waysignificant to those actions, includingenclosures, surfaces, channels, ambiences andobjects. Further, the descriptions must includethe cyclical and secular changes in thosespatial distributions, the control of space, andthe perception of it (p. 48).

In Appendix B (p. 349) of the same book,however, he warns that

while standard descriptions agree onemphasizing human activity in its relation tophysical form, they are prone to confound thetwo in a single ambiguous description, such assingle-family house or church. Is it a typeof building that is being denoted, or theactivities of worshipping or residing?

If interpreted broadly, his initial definition ofsettlement form encompasses the wholesubject of urban morphology. Yet his caveatalso points to the potential hazards implicit inour modes of description. Lynch is clearlystating that the fluidity between form and usein common names and descriptions, evenwithin specialist spheres, can be a barrier tounderstanding.

The potential for conflating different aspectsis not limited to form and use. Lynchsdefinition of form contains within it a numberof distinct features that should be made moreexplicit if descriptions, explanations andproposals are to be clear and coherent. Just asLynch has distinguished between the class ofphysical form and its relation to the classactivities, it is possible to examine theremaining parts of his definition in terms ofclasses, relations and properties.

Physical features which modify space insome way clearly refers to the class of


physical objects and their spatial relations,which, in a number of cases result in a patternof solid and void such as the interiors ofbuildings or patterns of streets and blocks.Enclosures, surfaces, channels andambiences (in the sense of surroundings)are different types of object or space createdby the spatial relation or arrangement ofobjects.

Persons doing things and flows ofpersons refer to the class of humans and theproperty of being engaged in some activity,including movement, and imply therelationship with the object or space thataccommodates the activity. The flow ofgoods and information refers to classes ofobject and the property of movement sharingthe relation of being directed by humans forhuman purposes.

The control of space and the perception ofspace are two different types of relationbetween a human (or group) and a space (and,by implication, part or all of the objects thatdefine the space). A space or object iscontrolled by someone or some group and,equally, perceived by someone or some group.The concepts of control and perception makeno sense without both sides of the relation.

Cyclical and secular changes in spatialdistribution refers to alterations in relationsbetween a class or object over time. The twobroad temporal relations are continuity andchange. Both change and continuity can onlybe described with reference to at least twostates of the same thing. What becomesimportant in describing the relations is theevidence we have for previous states in orderto describe the relation one way or the other.

Compressed within Lynchs concisedefinition of urban form are six distinctaspects:

physical form use/activities/movement control perception continuity/change movement or flow of materials and

information

Looking back at the definitions examinedpreviously, the first only explicitly includeduse, qualified by the relative position ofoccupants within a social structure (socialstatus). The second included both physicalform and use. The six aspects picked out byLynch, as already noted, cover most of thoseincluded within the discipline of urbanmorphology. For the purpose of determiningmore explicitly which aspects are included,four broad approaches to urban morphologycan be identified, each taking a slightlydifferent view of form:

spatial analytical configurational process typological historico-geographical

The spatial analytical approach

The spatial analytical approach is perhaps bestcharacterized by the work of Michael Battyand the Centre for Advanced Spatial Analysisat University College London. Using a rangeof methods and models including GIS, cellularautomata, agent based models and fractals,Batty seeks to understand the spatial structureand dynamics of cities as complex, emergentphenomena, in which global structure developsfrom local processes. Citing Jane Jacobs(1961, p. 349), Batty sees the city as a problemof organized complexity and applies theconcepts of emergence and evolution inmoving toward solving that problem.

The models employed and cited by Batty areopenly stated to have a loose correlation withthe scale of the phenomenon modelled (2007,pp. 35, 144-6). The models might representcity regions or areas within a city. Cells in amodel most appropriately represent plots orparcels or their simple aggregations but mightfall somewhere between parcels and censustracts or other administrative aggregationsdepending on the source of the data.

Similarly, the specific objects modelled areopenly left loose. In many cases they can beinterpreted to represent generic development


or built-up area and in some cases the modelsinclude routes. The concept of the neighbour-hood is fundamental to the functioning of thecellular automaton as a model but it is definedexplicitly in terms of the structure of the modelrather than the phenomena modelled.Importantly, there is ambiguity surroundingform and use in what is represented. Muchof the work cited by Batty deals with changes,growth and segregation of land uses as well asthe diffusion or migration of residentpopulations based on a range of factors (2007,pp. 142-3, 154) yet the morphologies thatemerge from the models most clearly resemblethe spatial distribution of urbanized areaswithin a sub-region (Figure 1). Indeed, Battystates that the models are not intended to

provide accurate or predictive descriptions butto strip the processes of city growth to theirbare essentials, and thus to uncover the basicmechanisms at work (2007, p. 109).

There seems to be a deliberate blurring ofthe aspects of physical form and use atdifferent spatial scales. Yet it would not seemto be outside the realms of possibility that,given an appropriate point of reference, themodels might be calibrated to complementmore accurately other forms of description.

The configurational approach

Space syntax represents the configurationalapproach to urban morphology, which seeks to

Figure 1. Graphic output from an agent-based computer model of a sub-regional urban system (reproduced from Batty, 2007, p. 253).


understand the spatial structure of settlementsthrough a range of analytical methods. At thescale of settlements, the theoretical basis of theapproach is the relationship between spatialstructure and the generic function ofmovement.

The... fundamental correlate of the spatialconfiguration is movement. This is the caseboth in terms of the determination of spatialform, in that movement largely dictates theconfiguring of space in the city, and in termsof the effects of spatial form, in that movementis largely determined by spatial configuration(Hillier, 1996, p. 152).

Like Batty, Hillier sees configuration asemergent, with global structure arising out oflocal processes.

With respect to the notion of form, spacesyntax takes a distinct view because of itsemphasis on space and spatial configuration,rooted in the analysis of buildings (Hillier andHanson, 1984). The concepts and analyticalmethods focus almost entirely on the voids ofa structure, principally the street spaces withina settlement, though some consideration isgiven to the spaces around buildings within aplot.

For Hillier, spatial form is the arrangementof spaces, with explicit reference to the

position of any given space within thestructure of the configuration as a whole. Thisformulation necessarily implies or assumes thesolid that defines the space or void. Thedifferent analytical techniques employedwithin the space syntax represent the structureof solid and void in different ways. In themore abstract techniques such as j-graphs, thesolid is not explicitly represented at all (Figure2). To make sense of the analysis, however,the solid must still be assumed to define thevoid. In the case of axial and convex spacemapping, the solids are explicitly drawn, or areat least used to generate the axial and convexmaps, and correspond to street-blocks (Figure3). It is important to note that axial andconvex space mapping are intended torepresent what can be seen by a human withina space. The approach therefore implicitlyincludes the relation between humans andphysical form. In terms of the aspects set outabove, space syntax includes:

space/physical form use/occupation/movement perception

The process typological approach

The process typological approach to urbanmorphology is rooted principally in the workof the Italian architect Saverio Muratori but isbest represented by the work of the architectand urbanist Gianfranco Caniggia, who studiedunder Muratori. The approach they developedseeks to inform their architectural and urbanproposals with an understanding of the builtenvironment by examining its detailedstructure and the historical process of itsformation. They begin with the generaldistinction between spatial and temporalrelations, which they refer to, respectively, ascopresence and derivation (Caniggia andMaffei, 2001, pp. 62-5). The analysis ofcopresence proceeds from an abstract set orschema of component subdivisions that formsa hierarchy: elements, structures of elements,systems of structures, and organisms ofsystems. This schema is first applied to indi-

Figure 2. Examples of j-graphs, whichillustrate the abstract connections and relative

positions of a spatial configuration(reproduced from Hillier, 1996 p. 102).


vidual buildings, with building materials suchas bricks, timbers, tiles etc. taken as theelements. The structures of elements are thenthe associations of building materials withinsuch things as walls, interior floors, roofs etc.Systems of structures are arrangements of thelatter into rooms, stairs, corridors etc., theorganism being the building. The samescheme is applied to towns, taking buildings aselements. The structure of elements is anassociation of buildings or an urban tissue, ingeneral referred to as an aggregate (Figure 4).The system of structures is then a combinationof tissues forming regions or districts, whichtaken together form the organism of the town(Caniggia and Maffei, 2001, pp. 73-4).

The forms found at the different levels areidentified as types which are conceived ascultural entities rooted in, and specific to, thelocal process of cultural development. Theoperation of the process over time and indifferent places leads to development andchange and diversification of forms. Functionis therefore implicit in the type concept in thatany form will have been initially conceivedand developed to satisfy a particular humanneed or desire. Throughout their texts,Caniggia and Maffei refer to the functions ofthe different types of forms at the differentlevels in the hierarchy. While different localprocesses lead to distinct forms, there is a

generic similarity to the process which ischaracterized as derivation. At the time ofconstruction, the form of a building is basedon an idea or concept derived from the sharedexperience of previous buildings ormodifications of them. The idea of thebuilding and the act of construction ormodification are thus essential parts of thecultural process and are distinct in terms ofclasses, relations and properties. The ideainvolves the relation between the sharedcultural concept and the population that holdsit and the act of construction involves therelation between the builders and what is built.Caniggia and Maffei thus identify thefollowing distinct aspects of urban form:

physical form function/use the idea of the building or form the act of construction/modification the cultural process of derivation and/or

development/change

The historico-geographical approach

The historico-geographical approach to urbanmorphology is rooted in and well summarizedby the work of the geographer M. R. G.Conzen. The aim of Conzens town-plan

Figure 3. Superimposed mapping of convex spaces and axial lines for part ofcentral London (reproduced from Hillier, 1996, p. 157).


analysis is to explain the geographicalstructure and character of towns through asystematic analysis of their constituentelements and development through time. Asset out in his seminal study of Alnwick (1969,pp. 3-5), he begins by distinguishing fivegeneral aspects:

site function townscape social and economic context development

Within the townscape, he distinguishes threeform complexes:

town plan land utilization pattern building fabric

The town plan is itself subdivided into threecomplexes of plan-elements:

street system plot pattern building pattern

The constituent element of the street-system isthe street; the element of the plot pattern is theplot and the element of the building pattern isthe block-plan of the building. Further,distinct combinations of streets, plots, andblock-plans are identified as plan-units (Figure5).

Looking at the five general aspects in termsof classes, relations and properties, functionand social and economic context are bothbased on the relations of use or activitiesbetween humans and built form. Function ismore limited and specific to particular classes

Figure 4. The formation of urban tissue or aggregates in differentgeneralized situations (reproduced from Caniggia and Maffei,

2001, p 130).


of activities, for example residential orcommercial. The social and economic contextis the combination and interaction of differentactivities and functions over a wider area. Inthis respect any given function is a part ofthe social and economic context. Site isdefined principally in terms of the spatialrelations and distribution of natural physicalfeatures such as geology, topography,hydrology and vegetation. As with Lynchschange, the process of development involvesthe temporal relations between elements and

aspects from one time to the next. Examination of the townscape as defined by

Conzen raises a number of ambiguitiesconcerning the element of the plot. Despitefunction having been identified as a distinctgeneral aspect, the townscape includes theform complex of land utilization pattern withthe plot identified as a unit of land use(Conzen, 1969, pp. 5, 79, 128). The town planalso includes the element complex of the plotpattern. The plot is thus defined in terms ofboth land use and physical form. This raises

Figure 5. Examples of plan units: Alnwick, Northumberland(reproduced from Conzen, 1969, p. 72).


the issue flagged up by Lynch of conflatingform and use and therefore blurring orobscuring the dynamic associations betweenthe two. Conzen himself openly recognizesthe importance of these links, noting that

town plan and to a lesser extent building fabricare conservative in that they tend to reflect thepattern of past landownership and capitalinvestment longer ... The land-use patternresponds more easily to changing functionalimpulses (Conzen, 1981, p. 80).

To be more consistent, the categories of socialand economic context, function and landutilization pattern, which are all defined bythe human-built form relation, would be betterincluded together as a separate aspect.

Conzens mention of land ownership in theabove quotation and illustration of propertyholdings in his study of Alnwick (Figure 6)raises a further point of ambiguity associatedwith the plot. In common use, the plot refersto a unit of property. As with form and use,there is the tendency to conflate the physicalform of plots and their status as an object ofownership or, more generally, control. Whilethe physical boundaries of plots generallycorrespond to the boundaries of control, it isnot always the case (Kropf, 1997). Morefundamentally, the concept of ownership andother forms of control involves a sociallydefined relationship between the controller andthe thing controlled. One does not make sensewithout the other. Just as with use, however,control is a fundamental aspect of urban formand is an essential factor in understanding theprocess of development. The issue of controlis the subject of an entire chapter in LynchsGood city form and is central to a number ofother works within the typological approach,in particular Habraken (1998), as well asMoudon (1986) and Castex et al. (1980, 2005).

In accord with the foregoing analysis,Conzens method identifies four principal aspectsof urban form:

site social and economic context, function, land

utilization townscape development.

The further aspect of control is implied byConzen in the identification of the plot as anelement. This is reinforced by the explicitinclusion of control as an aspect by otherswithin related approaches.

The case for physical form as the referenceaspect

The results of the analysis are presented inTable 1, which groups the different aspects bygeneral class and relationship, the four broadgroups being spatial relation of physicalobjects, interrelations between humans and

Figure 6. The pattern of pre-industrialproperty holdings in Alnwick, Northumber-

land (based upon Conzen, 1969, p. 35).


Table 1. General aspects of urban form as identified in the various approaches to urbanmorphology

Spatial relations of physical features

Site/environment Spatial relations of natural features unaltered by humans (the substrateof built form).

Built form Spatial relations of features built or modified by humans, encompassingboth solid and void and including planted vegetation.

Interrelations between humans and physical features

Social and economic context/local culture

Collective relations between human activities and between humanactivities and physical forms.

Function/use/activity Relations between humans and physical forms for particular purposesincluding movement and occupation.

Control (e.g. ownership) Socially acknowledged relations between an individual or group and aphysical form conferring powers of action and determination over theform.

Intention/design The sense or mental image motivating the modification or constructionof built form including representations such as drawings.

Construction The act of modifying or constructing built form.

Perception Mental and physiological response or experience of being in a place andthe image or sense retained in memory.

Flows of resources

Natural Sunlight, wind, water etc.

Human The movement of goods, information, energy, waste.

Temporal relations

Change/development Short-term cyclical changes in patterns of activity and long termtransformation of the natural and built environments necessarilydescribed in terms of states at two or more points in time.

physical form, flows of resources and temporalrelations. The different aspects are thendistinguished by the specific classes andrelationships. The aspect of resource flows,which is included by Lynch as a distinct partof built form, is noted and very usefullyelaborated by Osmond (2008), as is theimportance of vegetation.

The aim here is not, however, to set out acomprehensive set of aspects. It is to identifywhich amongst the commonly identified

aspects provides the best reference key orregistration mark for co-ordinating the otheraspects so that different descriptions can becorrelated in a rigorous way. Whicheveraspect is chosen, if it is to function as thereference key, it should be common to all theapproaches and defined consistently as distinctfrom other aspects in order to avoid theproblems of conflation.

Of all the aspects identified, physical formand use are common to all the different


approaches. There is, however, an importantdistinction between these two aspects that is anessential consideration for choosing areference aspect that can be defined in a waythat is consistent, coherent and comprehensive.If defined strictly, physical form is the spatialrelations of physical objects. Function, useand activity are interrelations between humansand some physical form. When we refer touse, we talk about the use of some object orspace defined by objects within a town.Functions such as residential or employmentpresuppose the infrastructure, building andequipment that accommodate the activities. Itis this fact that leads to the tendency noted byLynch to conflate the two.

There is no question that activities and usescan be defined without reference to physicalform. But the very fact that activities such asresiding, worshiping, working and playing are,on their own, relatively fluid and flexible, bothin their constituent elements and where theytake place, means they are less suited as areference aspect. Use is more evanescent andchanges more quickly than form, as was longago noted by Conzen. Physical form is themost tangible and persistent of all the aspects.

A point related to the general persistence ofform relative to other aspects is the fact thatmost representations of settlements primarilydepict physical form. As the most tangible andubiquitous aspect, it is the easiest to representby drawing and other graphic means. In caseswhere other aspects are represented, such asproperty boundaries on cadastral maps, theultimate reference point is still physicalfeatures on the ground (Kropf, 1997). If weare to reconstruct the process of developmentof settlements, the source material with whichto do so is most likely to be representations ofphysical form.

The tangibility, ubiquity and persistence ofphysical form make it the most suited to act asthe point of reference for co-ordinating andcomparing aspects. This seems at once bothobvious and too simple and naive to justifymention. But the cost of the neglect of such afundamental matter is a field of enquiry, takenas a whole, that is surprisingly incoherent andunco-ordinated. Consolidating the insights of

different groups to build a more effective bodyof knowledge and understanding is extremelydifficult.

Pertinent features of physical form

Focusing on physical form as a referenceaspect out of a range of co-dependent aspectsof urban form is not as simple as it mightappear. If it is obvious that physical formshould be the point of reference, it is equallyobvious that the physical form of humansettlements itself presents a diversity ofaspects. The different approaches to the studyof form tend to abstract different features ofphysical form as pertinent to theirinvestigations and represent them in differentways. At a general level, features andrelations include the following:

Features line (net) area/patch space module (solid/void)

Relations between features network patchwork

aggregate clustercellular matrix (aggregate of uniformdefined planes)fractal

hierarchy palimpsest

To an extent, the different approaches can becharacterized by the features they take aspertinent and the relations between them:

spatial analytical (patch, aggregate cluster,matrix)

configurational (line, space, network) process typologogical (module, modular

hierarchy) historico-geographical (area or patch, patch

hierarchy, palimpsest)

Just as all of the different aspects of urban


form are co-dependent facets of the samephenomenon, the different features andstructures are different views of the sameaspect. As such, there must be points ofcontact when different views are overlaid.Finding those points of contact is the challengeto be met in seeking to co-ordinate thedifferent views so that they might worktogether and reinforce each other.

To put the issue in these terms is in someways to overstate the case. Identifyingcommon features to use as the registrationmark should not be a major intellectual feat.The analogy with multi-plate printing impliedby the term registration mark can be used asa pragmatic methodological pointer. If thedifferent aspects of urban form and thedifferent features of physical form are seen asdifferent colours, each with its own patternapplied to a separate plate, it is the registrationmarks applied to each plate that make itpossible to co-ordinate the printing of all theplates and generate a coherent image.

The analogy is plausible in the first placebecause virtually all of the approaches to urbanmorphology make use of two-dimensionalgraphic representations of urban form,typically using the conventions of ortho-graphic projection in plan. For the analogywith printing to work, the first obviouspractical point to acknowledge is that all thedifferent aspects need to be shown from thesame point of view at the same scale. As inprinting, the registration marks might theneven be independent of the image and worklike a grid reference in mapping. The benefitof a reference aspect that is part of the image isthat it is always there to be used whatever theview.

Conclusion

It may seem perverse to pick apart urban formonly to try to put the pieces back together. Toa large extent, however, this is the essence ofmorphology. The purpose of the analysis andsynthesis is not to compile an exhaustive tableof deracinated parts. To go beyond a mindlessdisassembly, there is an absolutely essential

third component to the process which iscomparison. To a large extent comparison isat the core of perception and operates at asubconscious level. Goethes brilliance was tobring that intuitive capacity into consciousapplication. He compared one form withanother. He compared the different compo-nent parts and their relationships and hecompared the different stages in thedevelopment, growth and transformation offorms. He also overlaid and compared theinformation about the forms provided bydifferent fields and disciplines.

What emerges from the process is afundamentally composite view that isconceptually more integrated and articulated asa whole than the view provided by any singleperspective. For Goethe, these were neverpurely mental abstractions but essentiallybased on experience. Nor were they staticconceptions but capable of modification asnew forms were investigated through cycles ofhypothesis, deduction and induction (Wilkin-son, 1962, pp. 177-8). This paper has soughtto apply this method to urban form itself byundertaking a deductive and comparativecritical analysis of key texts from the differentapproaches to urban morphology. The resulthighlights that there are at least four broadtypes of aspect and eleven logically distinctgeneral aspects:

spatial relations of physical featuresnatural physical formbuilt physical form

interrelations between humans and physicalfeatures

social and economic contextuse/function/activitycontrolintentionconstructionperception

flowsnaturalhuman

changeformation/transformation/cyclical change

At first sight this may appear unduly


complicated. The provisional list of aspectsmust, however, be seen in the context of thephenomena that we are seeking to understand.If we acknowledge that cities are almostintractably complex and diverse, can weexpect to have a simple explanation for themthat can be understood at a single sitting? Theanalysis shows there is a clear logical basis forthe distinctions. If they are to have explanatoryvalue we need to identify how they fit togetherin some coherent way, not just statically, butas part of a process of formation and trans-formation. And just as it is comparison thatallows us to distinguish the aspects, it isfurther comparison that is necessary todetermine how they fit together.

Identifying consistently defined aspects ofform only clears the ground for and facilitateslooking in more detail at the individualaspects, comparing them and investigatingtheir interrelationships, associations andcorrespondences in order to identify the partthey play in the processes of formation andtransformation of urban form.

What is also clear from the results set outhere is that further comparison and criticalanalysis is needed, especially on the aspect ofphysical form, not only to determine how itmight best function as a reference key but alsoto ensure that our view of physical form is ableto pick up the full range and diversity ofspecific forms and features and the relation-ships between them.

One starting point would be to confront theambiguity that dogs particular features such asthe plot and find their place in the overallstructure of elements. Some initial work inthis direction shows positive results (Kropf,1996, 1997, 1998). Another starting pointwould be to fully acknowledge the differenttypes of overall structure that can be identifieddepending on the base elements chosen aspertinent. The most obvious examples ofdifferent structures are the network patterns oflinear features identified in the configurationalapproach, the patch hierarchies of morpho-genetic regions in the historico-geographicalapproach and the modular hierarchies of theprocess typological approach.

Are these views mutually exclusive or can

they be correlated by the use of a reference keyfor rigorous and consistent comparison?Using physical form as a common referenceaspect to co-ordinate different descriptions ofurban form would be a significant step towardbuilding a more coherent understanding ofhuman settlements. The alternatives wouldseem to be either viewing human settlementsas indivisible wholes or discrete and irrecon-cilable parts. If urban form remains mono-lithic we must be satisfied with a fascinatingbut ultimately mysterious phenomenon. If weseparate aspects but leave them isolated andfree-floating, we must be content withlistening simultaneously to a number ofunrelated conversations.

References

Batty, M. (2007) Cities and complexity (MIT Press,Cambridge, MA).

Burgess, E. W. (1925) The growth of the city, inPark, R. E., Burgess, E. W. and Mackenzie, R.D. (eds) The city (University of Chicago Press,Chicago) 47-62.

Calhoun, C. J. (ed.) (2002) Dictionary of socialsciences (Oxford University Press, Oxford).

Caniggia, G. and Maffei, G. L. (2001) Archi-tectural composition and building typology:interpreting basic building (Alinea, Florence).

Castex, J., Celeste, P. and Panerai, P. (1980)Lecture dune ville: Versailles (Editions duMoniteur, Paris).

Castex, J., Depaule, J. C., Panerai, P. and Samuels,I. (2005) Urban forms: the death and life of theurban block (Architectural Press, Oxford).

Conzen, M. R. G. (1966) Historical townscapes inBritain: a problem in applied geography, inHouse, J. W. (ed.) Northern Geographicalessays in honour of G. H. J. Daysh (Departmentof Geography, University of Newcastle uponTyne) 56-78.

Conzen, M. R. G. (1969) Alnwick, Northumber-land: a study in town-plan analysis (Institute ofBritish Geographers, London) revised edn.

Conzen, M. R. G. (1981) Geography and towns-cape conservation, in Whitehand, J. W. R. (ed.)The urban landscape: historical development.Papers by M. R. G. Conzen Institute of BritishGeographers Special Publication 13 (AcademicPress, London) 75-86.

Dennett, D. (1995) Darwins dangerous idea(Penguin, Harmondsworth).


Eco, U. (1979) A theory of semiotics (IndianaUniversity Press, Bloomington).

Goethe, J. W. (1952) Goethes botanical writingstranslated by Bertha Mueller (University ofHawaii Press, Honolulu HI).

Gould, S. J. (1991) Bully for brontosaurus(Penguin, Harmondsworth).

Habraken, N. J. (1998) The structure of theordinary (MIT Press, Cambridge, MA).

Helm, J. and Robinson, A. (2002) GCSEGeography for AQA Specification B(Heinemann, Oxford).

Hillier, B. (1996) Space is the machine (CambridgeUniversity Press, Cambridge).

Hillier, B. and Hanson, J. (1984) The social logic ofspace (Cambridge University Press,Cambridge).

Hoyt, H. (1939) The structure and growth ofresidential neighborhoods in American cities(Federal Housing Administration, WashingtonDC).

Jacobs, J. (1961) The death and life of greatAmerican cities (Random House, New York).

Kropf, K. (1996) Urban tissue and the character oftowns, Urban Design International 1, 247-63.

Kropf, K. (1997) When is a plot not a plot:problems in representation and interpretation,unpublished paper presented to the FourthInternational Seminar on Urban Form,Birmingham, England, July.

Kropf, K. (1998) Plot types and housing innineteenth century Westminster, in Petruccioli,A. (ed.) Rethinking the XIXth century city (AgaKhan Program for Islamic Architecture atHarvard University and the MassachusettsInstitute of Technology, Cambridge, MA) 113-19.

Kropf K. (2001) Conceptions of change in thebuilt environment, Urban Morphology 5, 29-42

Levy, A. (1999) Urban morphology and theproblem of the modern urban fabric: somequestions for research, Urban Morphology 3,79-85.

Lynch, K. (1981) Good city form (MIT Press,Cambridge, MA).

Moudon, A. V. (1986) Built for change (MIT Press,Cambridge, MA).

Osmond, P. (2008) An enquiry into newmethodologies for evaluating sustainable urbanform, unpublished PhD thesis, University ofNew South Wales.

Peirce, C. S. (1958) Charles S. Peirce: selectedwritings (Dover Publications, New York).

Putnam, H. (1995) Pragmatism (Blackwell,Oxford).

Slater, T. R. (1982) Urban genesis and medievaltown plans in Warwickshire andWorcestershire, in Slater, T. R (ed.) Field andforest: an historical geography of Warwickshireand Worcestershire (Geo Books, Norwich) 173-202.

Stanilov, K. and Scheer, B. C. (eds) (2004) Sub-urban form: an international perspective(Routledge, London).

Steadman, P. (2008) The evolution of designs(Routledge, London).

Whitehand, J. W. R. and Carr, C. M. H. (2001)Twentieth-century suburbs: a morphologicalapproach (Routledge, London).

Whitehand, J. W. R. and Morton, N. J. (2003)Fringe belts and the recycling of urban land: anacademic concept and planning practice,Environment and Planning B: Planning andDesign 30, 819-39.

Wilkinson, E. M. (1962) Goethes conception ofform, in Wilkinson, E. M. and Willoghby, L. A.(eds) Goethe: poet and thinker (Edward Arnold,London) 167-84.

The Codes Project

This project is a compilation of the codes, laws andrelated documents that have created, or sought tocreate, particular urban forms. Code is broadlydefined: it includes not only legal documents butalso social customs in other words, both legally-binding codes and customs that may not haveinvolved a governing authority. These documentsprovide a rich resource for urban planners,architects and others.

A website had been set up (http://codesproject.asu.edu/) to which all are invited to

contribute. Types of codes that are beingcontributed include unified development codes,architectural codes (building scale designregulations), building codes (health and safetyregulations), state enabling legislation, designguidelines, pattern books and master plans.

Further information is available from ProfessorEmily Talen, Arizona State University, PO Box875302, Tempe AZ 85287-5302, USA (E-mail:[email protected]).

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