Chapter 2 The Structure and Form of Urban Settlements

Transcription

1 Chpter 2 The Structure nd Form of Urbn Settlements Elen Besussi, Nncy Chin, Michel Btty, nd Pul Longley This chpter introduces you to the different theoreticl nd methodologicl pproches to the understnding nd mesuring of urbn growth nd urbn ptterns. Prticulr ttention is given to urbn sprwl s one of the forms of suburbniztion. Urbn sprwl tody represents chllenge for both scientists nd decision mkers, due to the complexity of its genertive processes nd impcts. In this chpter, we introduce wys of mesuring the sptil pttern of sprwl noting how remotely sensed imgery need to be integrted with sptil socioeconomic dt, nd how this integrtion is essentil in mking ccurte interprettions of very different urbn morphologies. Lerning Objectives Upon completion of this chpter, you should be ble to: Speculte on the rnge of processes which generte urbn growth nd its different structures Differentite between pproches used to define nd mesure urbn nd suburbn ptterns Describe some of the zone-bsed sptil sttisticl methods vilble to mesure urbn growth dynmics nd ptterns E. Besussi (*) Development Plnning Unit, University College London, 34 Tvistock Squre, London, WC1H 9EZ, UK e-mil: e.besussi@ucl.c.uk N. Chin nd M. Btty Centre for Advnced Sptil Anlysis, University College London, 1-19 Torrington Plce, London WC1E 7HB, UK e-mils: n.chin@ucl.c.uk; m.btty@ucl.c.uk P. Longley Deprtment of Geogrphy, University College London, Gower Street, London WC1E 6BT, UK e-mils: p.longley@geog.ucl.c.uk T. Rshed nd C. Jürgens (eds.), Remote Sensing of Urbn nd Suburbn Ares, Remote Sensing nd Digitl Imge Processing 10, DOI / _2, Springer Science+Business Medi B.V

2 14 E. Besussi et l. 2.1 Urbn Structure nd Urbn Growth: An Overview of Theories nd Methodologies trditionl urbn theories investigte how cities develop nd grow through systemtic interctions of infrstructures, people nd economic ctivities Cities emerge nd evolve from the colescence nd symbiotic interction of infrstructures, people nd economic ctivities. These interctions re systemtic, generlly in tht they re relted to development in the globl economy, nd more specificlly in tht they mnifest building nd trnsport technologies. But these interctions re lso sensitive to locl context, in tht settlements re individully resilient to constrints in their evolutionry pth. Given dvnces in technology, nd the sheer scle nd pce of contemporry urbn growth, the most rpid chnges in urbn form, pttern nd structure, re tking plce where historicl roots re wekest s in the recent suburbs of long estblished Western cities, or in the new cities of developing countries. A city like London would never hve been ble to develop its contemporry form, skyline, nd density of ctivity were it not for technologicl innovtions such s its underground trnsport network nd its role in globl finncil mrkets. Yet there re locl nd institutionl fctors such s the role of green belt plnning policy, peculir to the UK tht hs prevented the kind of sprwl chrcteristic of North Americn cities tking hold throughout the functionl region. Trditionl urbn theories investigte how cities develop nd grow through these kinds of interctions, nd in mcro terms re bsed on dvntges tht co-loction (i.e., the physicl loction where urbn nd economic ctivities re in close sptil proximity to one nother) cn offer to economies nd societies. Agglomertion economies, defined by those economic production systems tht benefit from coloction, hve been identified s key forces t work in the growth of cities t ny time nd in every plce. However, over the lst hlf century our trditionl understnding tht the only outcomes of these forces should be n ccelerting concentrtion of popultion, infrstructures nd jobs hs been chllenged by the evidence of de-concentrtion, first in the United Sttes nd now in Europe. The migrtion of griculturl popultions into the city which hs been centuries old fctor in rurl depopultion nd the dominnt force in creting urbn gglomertions is now giving wy to reverse migrtion into the countryside, t lest in mny western cities, s suburbniztion nd sprwl become the modus operndi of urbn growth. Of course, the inerti in the skeletl structure of the built form of the city in its buildings nd streets re importnt principlly becuse they ccommodte the loci of ctivities of urbn popultions. There is nerly century of interest in understnding the socio-sptil differentition of urbn popultions, tht cn be trced bck to the 1920s in the work of Prk, Burgess nd the Chicgo School of urbn ecologists, if not before in the writings of Mx Weber nd his nineteenth century contemporries. Here gin, urbn reserch hs focused upon the generl s well s the specific. The clssic ringed socio-economic structure of 1920s Chicgo, for exmple, ws

3 2 The Structure nd Form of Urbn Settlements 15 deemed by the Chicgo School to be mnifesttion of generl biotic nd culturl forces (which led to the term urbn ecology ), constrined by the prticulr physicl setting of the city. Underpinning these physicl structures nd loctionl ptterns is trnsporttion. Cities exist lrgely becuse trnsporttion to ccessible nodes in spce provides the rtionle for the gglomertion economies tht define them. Sprwl for exmple is loosely ssocited with the trdeoff between the desire to live s close to the city s possible ginst the desire to purchse s much spce s possible nd still retin the benefits of urbn or suburbn living. Sprwl thus comes bout through rising welth nd trnsporttion technologies tht llow such suburbn development nd urbn morphologies to reflect this trdeoff. The dynmics of the processes defining such sptil interction nd lnd development re thus centrl to n understnding of urbn form nd structure. In both physicl nd socio-economic terms, the wys in which urbn phenomen re conceived very much determines the wys in which they re subsequently mesured nd then nlyzed. Studies concerned principlly with urbn extent (such s inventory nlysis focusing upon the wys in which the countryside might be gobbled up by urbn growth) tend to be guided by definitions of the extent of irreversibly urbn rtificil structures on the surfce of the Erth. Such structures support rnge of residentil, commercil, industril, public open spce nd trnsport lnd uses. Remote sensing clssifiction of surfce reflectnce chrcteristics llows the cretion of simple, robust nd directly comprble mesures of the dichotomy between nturl nd rtificil lnd cover (red reltive discussions in Chpters 3 5). Of course, such urbn development is not necessrily entirely contiguous nd, s shown in Chpter 8, techniques of GIS cn be used to devise pproprite contiguity nd sptil structure rules. In this strightforwrd sense, it is possible to formulte firly robust nd objective indictors of clss nd extent through the sttisticl clssifiction of lnd cover chrcteristics nd sptil ptterning of the size, shpe nd dimension of djcent lnd use prcels. These indictors cn provide useful nd direct mesure of the physicl form nd morphology of urbn lnd cover tht is very useful in delineting the extent of individul urbn settlements nd in generting mgnitude of size estimtes for settlement systems (Btty nd Longley 1994). Chpter 7 of this book describes how developments in urbn remote sensing hve led to the deployment of instruments tht re cpble of identifying the reflectnce chrcteristics of urbn lnd cover to sub-meter precision (lso see Donny et l. 2001; Mesev 2003). In ddition to direct uses, remotely sensed mesures re lso of use in developing countries where socioeconomic frmework dt such s censuses my not be vilble. For resons tht lie beyond the scope of this underpinning the skeletl structure of the built form of the city is trnsporttion remote sensing cn provide useful nd direct indiction of the physicl form nd morphology of urbn lnd cover in cities remote sensing represents complementry dt source to trditionl socioeconomic surveys

4 16 E. Besussi et l. chpter, improvements in the resolution of stellite imges hve not been mtched by commensurte improvement in the detil of socioeconomic dt on urbn distributions. This cretes something of n symmetry between our incresingly detiled understnding of built form nd our bility to mesure the detil of intr urbn socioeconomic distributions (nd we should not forget tht built form is lso mesurble through ntionl mpping gency frmework dt (Smith et l. 2005). However, remote sensing nd socioeconomic sources incresingly present complementry pproches, in tht tody s high-resolution urbn remote sensing dt my lso be used to constrin GIS-bsed representtions of socioeconomic distributions (Hrris nd Longley 2000). There is considerble reserch in the ptterning of cities but much of this hs been focused on explining urbn structure nd form t single point in time, s if cities were in some sort of perpetul equilibrium. Clerly the bsence of rigorous dt through time hs been mjor constrint on our bility to mnufcture n pproprite science of urbn dynmics nd thus most of the thinking bout urbn chnge hs been specultive nd non rigorous. This is chnging. New dt sets, concern for intrinsiclly dynmic issues such s how to control nd mnge urbn sprwl rther then simply worrying bout the sptil rrngement of growth, nd new techniques such s urbn remote sensing which re being fst developed to process routine informtion from stellite nd eril photogrphic dt, re becoming importnt. This book will del with these techniques in considerble detil but in this chpter we will set the context in illustrting the kinds of issues tht re involved in understnding the most significnt spects of contemporry urbn growth: suburbn development nd sprwl. In the next section we will exmine the physicl mnifesttion of suburbniztion nd this will set the context to discussion of urbn sprwl in Europe where we will focus on how it might be mesured nd understood. 2.2 Physicl Mnifesttions of Urbn Growth: Suburbniztion nd Sprwl Whether we envision vst swthes of single-fmily detched houses, ech surrounded by grden nd equipped with swimming pool s in mny prts of North Americ, suburbniztion is the distinctive outcome of contemporry urbn growth the much more frgmented nd diversified low density fringes of Europen cities, or the seemingly uncontrollble slums sprwling round the cpitl cities in developing countries, it is cler tht suburbniztion is the distinctive outcome of contemporry urbn growth. Urbn sprwl is by no mens restricted to ny prticulr socil or economic group or ny culture or indeed ny plce. It is lrgely the results of growing popultion whose loction is uncoordinted nd unmnged, driven from the bottom-up nd subject to ggregte forces involving control over the mens of production whose impct we find hrd to explin in generic terms.

5 2 The Structure nd Form of Urbn Settlements 17 In the following discussion, we will focus upon urbn sprwl s defining chrcteristic of urbn development nd growth. Given the difficulties inherent in mesuring nd monitoring physiclly-mnifest socioeconomic structures, set out bove, we will dopt wht is essentilly physiclist definition of sprwl s the rpid nd uncoordinted growth of urbn settlements t their urbn fringes, ssocited with modest popultion growth nd sustined economic growth. Wht is prticulrly interesting bout urbn sprwl is less the quest for n ll-encompssing definition of its cuses nd mnifesttions, thn the chllenge it represents for the theoreticl nd scientific debtes. In this respect the fields of science interested in collecting nd structuring empiricl evidence of urbn growth through remote sensing re becoming incresingly importnt. When it comes to defining nd nlyzing urbn sprwl, urbn theories, whether trditionl or emergent, descriptive or normtive, conflict with ech other on lmost everything, from their conception nd rtionle, through to the mesurement of sprwl nd the recommended policy ssessment nd nlysis which such theories imply in its control. While we hve defined urbn sprwl in generl terms, its exct locl connottions will lwys likely be debtble. From this stndpoint, s Ewing (1994) implies, it is often esier to define sprwl by wht it is not. It is sometimes implicitly defined by comprison to the idel of the compct city, nd for the most prt, emerges s its poor cousin. The consequences of urbn sprwl remin hot topic of policy concern, most often becuse of its perception s force eroding the countryside, which mrks the finl pssing of n urbn rurl world into n entirely urbnized one (see Chpter 3 in this volume) with ll the negtive connottions tht this implies for the visul environment, s well s growing concern for the impcts posed to long-term urbn sustinbility. Though these concerns re not new, the lst 20 yers of economic growth hs fuelled not only rpid urbn expnsion but ssocited problems such s crime, unemployment, nd locl government budget deficits which re ll connected to the contrst between the sprwling periphery of the city nd its inner decline. Urbn sprwl hs thus become mjor contemporry public policy issue. During much of the twentieth century, the control of urbn growth hs been of mjor concern to plnning gencies who hve sought to control peripherl development through vriety of rther blunt instruments such s green belts nd strict development controls which were designed to stop growth. But s contemporry ccounts of urbn sprwl illustrte (Hyden 2004), these instruments hve been lrgely ineffective nd now the focus is on much more informed nd intelligent strtegies for deling with such growth. Contemporry urbn strtegies focus more on sustinbility of development under different economic scenrios nd hve come to be clled strtegies for smrt growth. We hve come to the understnding tht growth cn never be stopped per se nd thus peripherliztion of cities is likely to continue for it is unlikely tht even the most drconin strtegies to urbn sprwl is generlly defined s the rpid nd uncoordinted growth of urbn settlements t their fringes smrt growth denotes rnge of urbn strtegies tht focuses on sustinbility of development under different economic scenrios

6 18 E. Besussi et l. control sprwl will led to high density, compct nd more constrined cities, t lest in the foreseeble future. Much of the confusion over the chrcteristics nd impcts of sprwl stems lrgely from the indequcies of definition. However it is illusory to believe tht more dt locl connottions of urbn sprwl re highly dependent on the culturl, geogrphic nd politicl context where sprwl is tking plce whether remotely sensed or census bsed cn help in solving the debte over wht sprwl is or is not, nd whether it hs only negtive or lso some positive impcts. Definitions of sprwl re highly dependent on the culturl, geogrphic nd politicl context where sprwl is tking plce to the point where wht is perceived s suburbn sprwl in Europe might be described s dense nd urbn in the US. Differences lso exist between different Europen countries due to their different histories of lnd use plnning. This is to sy the solution to the problem of defining urbn sprwl does not rest on more dt nd better methods to tret them, but in the mening tht is ssigned to it in different contexts nd times. To this purpose the importnce of urbn sprwl in the public policy gend hs generted n re of misunderstnding between descriptive nd explntory pproches on one side nd normtive ones on the other. This is much broder issue thn cn be ddressed within the limits of this chpter, but it should be kept in mind when exploring the literture tht hs been developing round urbn sprwl in the lst 20 yers. Often, sprwl hs been defined in terms of its negtive effects nd impcts, even though these re sometimes tken s underlying ssumptions rther thn empiriclly demonstrted fcts. Here we will present some possible definitions of urbn sprwl bsed on form, density nd lnd use ptterns. As cvet, it must be noted tht none of these pproches lone cn identify urbn sprwl, rther sprwl is comprised of combintion of multiple spects. Cuses of sprwl (e.g., chnging loction preferences nd decresing costs of privte individul trnsport, for exmple) nd its impcts (e.g., lnd consumption, trffic congestion, socil segregtion bsed on income or ethnic origins) should lso be tken into ccount, especilly if the purpose of definition is to support the design of policy mesures to tckle urbn sprwl. We will subsequently illustrte these issues t the end of the chpter with reference to the EU SCATTER project Defining Sprwl Through Form The term urbn sprwl hs been used to describe vriety of urbn forms, including contiguous suburbn growth, liner ptterns of strip development, nd lepfrog or scttered development. These forms re typiclly ssocited with ptterns of clustered, non-trditionl centers bsed on out of town mlls, edge cities, nd new towns nd communities (Ewing 1994; Pendll 1999; Rzin nd Rosentrub 2000; Peiser 2001). These vrious urbn forms re often presented in the literture s poorer, less sustinble or less economiclly efficient sprwling forms cn be considered to lie long continuum from firly compct to completely dispersed developments

7 2 The Structure nd Form of Urbn Settlements 19 Tble 2.1 Types of sprwl Type High density Low density Compct contiguous Circulr or rdil using mss trnsit Possible but rre? Liner strip corridor Corridor development round mss trnsit Ribbon development long rdil routes Polynucleted nodl Urbn nodes divided by green belts Metro regions with new towns Scttered/discontiguous Possible but rre? Metro regions with edge cities lterntives to the compct idel of urbn development. In prctice sprwling forms cn be considered to lie long continuum from firly compct to completely dispersed developments. A vriety of urbn forms cn be described using typology bsed on two continuous dimensions, which here re mde discrete for explntory purposes: settlement density (high nd low) nd physicl configurtion (rnging from contiguous nd compct to scttered nd discontiguous). This clssifiction system suggests the eight idelized types of sprwl which re presented in Tble 2.1. Glster et l. (2001) hve lso clssified the physicl forms ssocited with urbn sprwl into types (Fig. 2.1) nd which need to be viewed in the context of the typology presented in Tble 2.1. This clssifiction lso ccommodtes considertions of physicl configurtion nd density. This method clssifies ptterns of urbn sprwl ccording to eight components: density, continuity, concentrtion, clustering, centrlity, nuclerity, lnd use mix nd proximity. These mesures re demonstrbly useful to identify the mjor dimensions of sprwl. At the more compct end of the scle, the trditionl pttern of suburbn growth hs been identified s sprwl. Suburbn growth is defined s the contiguous expnsion of existing development from centrl core. Scttered or lepfrog development lies t the other end of the spectrum (Hrvey nd Clrk 1965). The lepfrog form chrcteristiclly exhibits discontinuous development some wy from historic centrl core, with the intervening res interspersed with vcnt lnd. This is generlly described s sprwl in the literture, lthough less extreme forms re lso included under the term. Other forms tht re clssified s sprwl include compct growth round number of smller centers (polynucleted growth), nd liner urbn forms, such s strip developments, long mjor trnsport routes. Indeed vocbulry of different vrieties of sprwl is fst emerging due to the fct tht growth everywhere seems to be somewht uncoordinted prticulrly on the periphery of the city (Hyden 2004). Sprwl in fct exists in very different forms which rnge from highly clustered centers edge cities in low density lndscpes to the kinds of edgeless cities tht exist where cities grow together into meg-poles of the kind tht re chrcteristic of western Europe nd even estern the vrious forms for urbn sprwl pose chllenge for urbn remote sensing Chin. The morphology of these structures rnges from rther distinct edges nd peripheries to somewht more blurred or fuzzy perimeters nd these vrious differences

8 20 E. Besussi et l. Compct Development Scttered Development Liner Strip Development Polynucleted Development Lepfrogging Development Fig. 2.1 Physicl ptterns defining sprwl (Glster et l. 2001) pose mjor plnning problem for urbn remote sensing which cn only be resolved by fusing socioeconomic dt into their interprettions. Another clssifiction is tht of Cmgni (Cmgni et l. 2002), who hs identified five types of suburbn development ptterns on the bsis of the level of lnd consumption tht ech type requires. This clssifiction seeks to guge impcts, nd lso mkes use of the sme criteri (e.g., density nd physicl configurtion) used in the previous two clssifictions (see Tble 2.2). The Cmgni clssifiction provides n idelized txonomy, nd rel world instnces of urbn sprwl development my be positioned on continuum pssing through these idelized types. We will present some of these rel cses below in our outline of the SCATTER model.

9 2 The Structure nd Form of Urbn Settlements 21 Tble 2.2 Types of suburbn development (Cmgni et l. 2002) (T1) in-filling, chrcterized by situtions where the building growth occurs through the in-filling of free spce remining within the existing urbn re (T2) extension which occurs in the immeditely djcent urbn fringe (T3) liner development tht follows the min xes of the metropolitn trnsport infrstructure (T4) sprwl tht chrcterizes the new scttered development lots (T5) lrge-scle projects, concerning the development of new lots of considerble size tht re independent of the existing built-up urbn re Defining Sprwl Through Lnd Use Lnd use ptterns provide second mens of describing urbn sprwl. A report from the US Trnsporttion Reserch Bord (1998) lists the chrcteristics of sprwl pertinent in the United Sttes setting s: low-density residentil development; unconstrined nd non-contiguous development; homogenous single-fmily residentil development with scttered units; non-residentil uses such s shopping centers, strip retil, freestnding industry, office buildings, schools nd other community uses; nd lnd uses which re sptilly segregted from one nother. Additionlly the report chrcterizes sprwl s entiling hevy consumption of exurbn griculturl nd environmentlly sensitive lnd, relince on the utomobile for trnsport, construction by smll developers, nd lck of integrted lnd use plnning. These chrcteristics re very brod-bsed nd typify lmost ll post-world urbn sprwl is sometimes chrcterized in terms of lnd use ptterns Wr II development in the United Sttes. Thus sprwl is lmost impossible to seprte from ll conventionl development (Trnsporttion Reserch Bord 1998, pp. 7). Unfortuntely, while this ensures tht no spect of sprwl is omitted, it does little to differentite sprwl from other urbn forms. Sprwl is most commonly identified s low-density development with segregtion (mesured t n pproprite scle) of uses; however, it is not cler which other lnd use chrcteristics must be present for n re to be clssified s sprwl (Btty et l. 2004). 2.3 The SCATTER Project A recent EU-funded project hs developed definition of sprwl tht is bsed on the environmentl, socil nd economic impcts of sprwl processes. The literture generlly ssumes tht these re negtive, perception tht is becoming common in Europe where urbn sprwl is much more recent nd rther differently differentited phenomenon thn in the United Sttes, nd where its emergence hs been ccompnied by n incresed public nd privte sensitivity towrds urbn sustinbility. The SCATTER Project (Sprwling Cities And TrnsporT from Evlution to Recommendtions) belongs to the sustinbility-oriented reserch nd policy ctions sponsored by the Europen Commission. Its min strting point is once

10 22 E. Besussi et l. Fig. 2.2 Urbn lnd use (drk gry) (from Remotely sensed dt (EEA, 1990) in the Six Europen city regions) gin rooted in the notion tht infrstructure, people nd economy interct nd tht trnsport infrstructures in prticulr ply key role in reinforcing or constrining sprwl processes. The min gol of the project is to evlute the impct of new trnsport infrstructures on sprwl processes nd to provide policy recommendtions to locl uthorities tht re willing to reduce sprwl nd its impcts. The SCATTER project nlyzes sprwl using both qulittive nd quntittive methods, nd considers smple of six Europen cities (Bristol, Brussels, Helsinki, Miln, Rennes nd Stuttgrt). Figure 2.2 shows the CORINE-bsed lnd use mps of these cities, bsed on the visul interprettion of Lndst nd SPOT stellite imges. In Fig. 2.3 we show the cities s we hve prtitioned them into dministrtive units where we record popultion nd relted economic chnge ssociting this with lnd cover chnge in Fig A number of models hve been developed for these cities where it is cler tht lthough ll size cities hve been chrcterized by physicl sprwl for the lst 40 yers, popultion nd employment hve not been continuously incresing. In Europe we re encountering phenomenon which hs long dominted North Americn cities, tht is, despite continued sprwl, economics nd popultion might ctully be declining in such sprwling cities. At this point, it is worth digressing little to note how urbn remote sensing might be ble to provide dt tht cn be complemented by trditionl socioeconomic dt.

11 2 The Structure nd Form of Urbn Settlements 23 Fig. 2.3 The SCATTER cse study cities (shown t the sme scle) In sense this is wht this entire book is bout, but such remote sensing is in its infncy nd, s discussed in Chpters 3 nd 6, s stellite technologies generte higher nd higher resolution imges, the possibility of getting much more uthorittive definitions of urbn boundries, nd different urbn lnd uses, enbles step chnge in our understnding of the ptterns nd dynmics of suburbn growth. The vrious chpters in this book illustrte the stte of the rt but good overview is provided by Mesev (2003) who shows tht incresing resolution through ever more elborte stellite imgery in fct is usully ccompnied by n incresing level of noise in the dt which tends to confuse interprettion. higher sptil resolution in remotely sensed imges is usully ccompnied by n incresing level of noise in the dt which tends to confuse interprettion Fusing of Remote Sensing Imges nd Socioeconomic Dt Cities re rtifcts tht exist physiclly nd socilly in terms of our own definitions nd these exist t different scles. As we get ever fine scle dt, the nture of the heterogeneity in sptil ptterning chnges nd fr from incresing our bility to detect lnd use more ccurtely, it often confounds this.

12 24 E. Besussi et l. This is why is it so importnt to fuse socioeconomic dt which is much more scle dependent in terms of the wy it is structured nd delivered to us thn is remotely sensed dt. Wys of enbling such fusion depends on new techniques for ingeniously ggregting nd disggregting dt, for overlying dt in diverse wys nd for clculting multiple indices of scle nd correltion which thence need to be interpreted in robust frmeworks. In fct one of the most difficult problems with new imgery t finer resolutions from the new genertion of irborne scnners nd stellites is tht the error structures in such dt re lrgely unknown nd thus new sttisticl theories re required before effective post processing of such dt sources becomes resilient (Smith 2004). This quest is only just beginning nd in terms of urbn morphology, socioeconomic ptterning is still more distinct thn physicl ptterning from remote sensing imgery Qulittive Anlysis of Urbn Sprwl in Europe As discussed in our introduction, generlized quntittive mesures of urbn form, obtined through urbn remote sensing, cn provide only prtil contribution to our understnding of the efficiency nd effectiveness of different urbn forms. The SCATTER project hs thus encompssed qulittive s well s quntittive nlysis. The purpose of the former ws to detect nd understnd the locl events nd plnning processes tht led to the emergence of urbn sprwl. The relevnce of these events nd processes in the decision gend of locl uthorities nd experts ws ssessed, s ws the overll level of wreness of this prticulr urbn phenomenon. This informtion is necessry if we wnt to complement quntittive mesures with n embedded understnding of sprwl tht is relevnt to plnners nd decision mkers. The objectives were therefore chieved by nlyzing interviews conducted with locl uthorities representtives nd experts in our six cse cities. The results of the qulittive investigtions quntittive mesures of urbn hve reveled tht policy mkers nd locl experts provide descriptions of urbn sprwl, which re quite phenomen from different from those vilble through literture review. remote sensing For this reson we hve found them vluble in our nd different censuses need to be reserch nd hve grouped them to build new typologies of sprwl. Although not centrlly relevnt to book complemented concerned principlly with remote sensing, it is pproprite to discuss them briefly here, in the interests of plnners nd deci- with input from blnce nd completeness of coverge (for full description of the methodology nd of the typology, see Besussi sion mkers nd Chin 2003). Policy mkers nd implementers essentilly see sprwl s:

13 2 The Structure nd Form of Urbn Settlements 25 Emergent polycentric region, chrcterized by the emergence or development of secondry urbn centers A scttered suburb, chrcterized by infill processes through which scttered nd low density housing developments locte between centers or round existing trnsport infrstructures Peripherl fringes, chrcterized by higher densities thn suburbn developments nd inhbited by popultions tht hve relocted becuse of the incresing costs of life in the urbn centers nd/or Commercil strips nd business centers, locted following rtionle bsed on ccessibility, low cost of lnd nd gglomertion economies Sttisticl Indictors to Identify nd Quntify Urbn Sprwl The objective of the sttisticl nlysis within SCATTER hs been to quntittively identify nd mesure urbn sprwl in the cse cities. The methodology dopted uses sttisticl techniques bsed upon shift-shre nlysis (see below), which re pplied to time-series of zonl dt. The dt used in the nlysis re minly popultion, employment nd verge commuting distnce. The method divides ech urbn region into two types of sub-regionl zoning systems. The first one consists of concentric res bsed on commuting ptterns, s illustrted in Fig. 2.4 for the Fig. 2.4 Concentric zoning system for Bristol urbn region

14 26 E. Besussi et l. Bristol region; this distinction ws bsed on percentge of commuters trveling dily towrds the core urbn re. The core urbn re is identified differently for ech of the cse cities, on the bsis of ntionl clssifiction methods while the first nd second rings (suburb nd hinterlnd) consist of zones where more or less thn 40% of commuters trips re directed towrds the core re. The second zoning systems, illustrted for ll six cities in Fig. 2.3, consist of sub-zones representing the smllest sttisticl unit for which consistent nd comprble dt re vilble. In the UK context, these sub-zones re bsed on wrds nd prishes nd ggregtions thereof. The generlized shift-shre method computes for ech smll sub-zone the growth rte of ech vrible (popultion, employment nd commuting distnces). In second step the devition of ech smll sub-zone s growth rte from the regionl growth rte is lso computed. In the SCATTER project the shift-shre method is used to identify the role plyed by the two growth components, the overll growth rte, l () t nd time depending fctor g i () t representing zonl devitions from the verge growth pth, in the ctul growth of ech smll zone. The nlysis is crried out in three steps: 1. Estimtion of the verge growth rte s 1 X ( t+ Dt) l ( t) = ln Dt X () t (2.1) where X ( t), X ( t+ D t) represent the totl volume of the vrible over the entire urbn region t times t nd t+ Dt respectively. 2. Estimtion of the zonl devitions of the verge growth pth s: g i 1 X + i ( t Dt) () t = ln l () t Dt Xi () t (2.2) 3. The estimted prmeters l () t nd g i () t my exhibit some noisy structure, due to possible dt uncertinties. Therefore pproprite dt filters re pplied to the men growth rtes nd the devitions of the growth rtes in order to smooth out such disturbnces. Tbles 2.3 nd 2.4 show the vlues of the prmeters for popultion nd employment growth rte in the six cse cities. The vlues re smoothed using Gussin moving verge procedure. The quntittive nlysis hs lso pplied more trditionl sptil sttisticl mesures, such s the indictors of locl nd globl sptil utocorreltion. For vlue of prticulr vrible (e.g., popultion density), indictors of sptil utocorreltion mke it possible to estimte whether zone i is surrounded by zones exhibiting very similr or very dissimilr vlues, or is surrounded by heterogeneous, ptchy pttern of similr nd dissimilr vlues. To identify locl sptiotemporl pttern of vribles the correltions between nerby vlues of the sttistics re derived nd verified by simultions. There re mny possibilities to test for the existence of such pttern. One of the most populr is Morn s I sttistic, which is used to test the

15 2 The Structure nd Form of Urbn Settlements 27 Tble 2.3 Temporl men vlue of l () t nd g i () t for popultion Smoothed l () t Smoothed g i () t Cities Yers Whole study re (%) Urbn centre (%) Outer urbn ring (%) Miln Brussels Stuttgrt Bristol Helsinki Rennes Hinter-lnd (%) Tble 2.4 Temporl men vlue of l () t nd g i () t for employment Smoothed l () t Smoothed g i () t Cities Yers Whole study re (%) Urbn centre (%) Outer urbn ring (%) Hinterlnd (%) Miln Brussels Stuttgrt Bristol Helsinki Rennes null hypothesis tht the sptil utocorreltion of vrible is zero. If the null hypothesis is rejected, the vrible is sid to be sptilly utocorrelted (see Anselin 1995; Getis nd Ord 1996 for theoreticl nd forml description of the indictors). As n exmple, when pplied to popultion density, locl indices of sptil utocorreltion might be used to define urbn centers (high utocorreltion of density between djcent units similr high densities), the rurl hinterlnd (high utocorreltion similr low densities), urbn poles (low utocorreltion urbn poles surrounded by rurl zones, with much lower densities), nd finlly intermedite zones chrcterized by very low sptil utocorreltion, corresponding to suburbn res, which re mix of more or less recently urbnized communes nd other still rurl communes. In Fig. 2.5 we provide mp of the locl indictor of sptil utocorreltion for the popultion densities in the SCATTER cse study cities. 2.4 Conclusions This chpter hs provided n overview of some of the issues tht re slient to the mesurement of urbn form nd function. In mny respects, urbn remote sensing provides n importnt spur to improving our understnding of the wy tht urbn res grow nd chnge. Certinly there is sense in which our bilities to routinely monitor incrementl ccretions nd chnges to urbn shpes re not mtched by socioeconomic dt of similr sptil or temporl grnulrity. Although incresingly

16 28 E. Besussi et l. Fig. 2.5 Sptil distribution of Locl Morn I for inhbitnts per squre kilometers detiled nd precise in sptil terms, very high resolution remote sensing imges of urbn res tell us rther little bout urbn lifestyles, unless supplemented by socioeconomic dt. This chpter hs set out some of the wys in which definitions of sprwl my be bsed upon quntittive mesures of urbn infrstructure nd qulittive impressions of the wy tht urbn policy evolves. An importnt chllenge is to ugment such quntittive nd qulittive mesures with generlized indices of urbn lifestyle (e.g., sprwling low density settlements suggest suburbn lifestyles). Tody there is no single urbn wy of life (if ever there ws) nd there is need for better nd more generlized understnding of lifestyles, since they my hold the key to understnding how individul cities evolve nd chnge within systems of cities. Severl chllenges rise from the use of remote sensing in the nlysis of urbn sprwl. More wys of fusing remotely sensed dt (see Chpter 11) with socioeconomic dt re required so tht the definition of different types of urbn morphology might be redily identified. The current stte of the rt is such tht the

17 2 The Structure nd Form of Urbn Settlements 29 edges of urbn lnd uses re lwys fuzzy nd this mkes ground truthing lmost impossible. Urbn plnning nd whole host of urbn model pplictions require much more ccurte dt thn remote sensing hs so fr been ble to deliver. Moreover, lthough there re now some quite good exmples of urbn remote sensing interprettion, nd lthough we hve quite long time series in mny plces going bck to the 1970s, for exmple, the qulity of this dt hs continully improved nd this mkes good time series nlysis tricky. Further, such imgery is still more pproprite in situtions where fst nlysis of rpid urbn growth is needed, for exmple, the exploding cities in developing countries. In developed countries, emerging developments in new remote sensing technologies such s LIDAR tht re fused with conventionl technologies re providing exciting developments t the locl scle (see Chpter 9). At the sme time, dding prior geometric informtion to such interprettions is providing impressive mens for dvncement in the field. These chllenges set context for pplictions of these new technologies presented in the rest of this book. Chpter Summry In this chpter you hve been introduced to key concepts nd theories on urbn growth nd how these hve pproched the nlysis nd mesurement of suburbniztion nd sprwl. The min ide is tht the contemporry city in both developed nd developing worlds needs much more thn just one theory or one method of nlysis or one typology of dt to be fully understood. The contemporry city, of which urbn sprwl is one of the most evident spects, is chllenge to trditionl nlyticl methods nd requires tht socil sciences interct with erth sciences, nd urbn economics with GIS in order to build coherent picture of ptterns nd trends of urbniztion. The pproch developed by the SCATTER reserch project nd presented in this chpter provides n exmple of n interdisciplinry method tht mixes qulittive nd quntittive methods to understnd sprwling settlements surrounding Europen cities nd to evlute the impct of trnsport on future development. Lerning Activities Lern to Identify Sprwl Using the Internet, serch for mps of different cities showing their urbn form nd structure nd lern the differences between sprwl in North Americ, Europe, developing countries, nd cities in other prts of the world. Below re some links you cn strt with:

18 30 E. Besussi et l. SCATTER Project: Modelling Lnd Use Dynmics: Erth Science Dt Interfce: index.jsp Using remotely sensed imges of different cities, reflect on nd identify significnt morphologicl differences tht tell you something bout the socil nd economic structure of ech city. Discuss with your instructor how the size of the re nd scle of nlysis mke difference. Study Questions Wht difference does the level of resolution of remotely sensed imge of n urbn re mke to your interprettion of its form nd structure? How cn socioeconomic dt such s tht from Popultion Census help you in mking good interprettions from remotely sensed imge which is overlid with such dt? To wht extent cn stte-of-the-rt remote sensing imgery enble you to detect different vrieties of trnsporttion systems in cities? To wht extent is city development constrined by physicl constrints? How cn lnd cover nlysis provide good representtions of such constrints? Cn remote sensing imgery enble you to mke coherent estimtions of urbn density? How? How cn informtion on the connectivity of n urbn re through the lyout of its physicl buildings nd street ptterns be fused into remote sensing dt so tht interprettions of urbn morphology my be enhnced? How cn zonl bsed dt be merged with pixilted dt from urbn remote sensing imges in GIS? References Anselin L (1995) Locl indictors of sptil ssocition LISA. Geogr Anl 27: Btty M, Longley PA (1994) Frctl cities: geometry of form nd function. Acdemic, Sn Diego, CA Btty M, Besussi E, Mt K, Hrts JJ (2004) Representing multifunctionl cities: density nd diversity in spce nd time. Built Environ 30: Besussi E, Chin N (2003) Identifying nd mesuring urbn sprwl. In: Longley PA, Btty M (eds) Advnced sptil nlysis. ESRI, Redlnds, pp Cmgni R, Gibelli MC, Rigmonti P (2002) Urbn mobility nd urbn form: The socil nd environmentl costs of different ptterns of urbn expnsion. Ecol Econ 40: Donny JP, Brnsley MJ, Longley PA (eds) (2001) Remote sensing nd urbn nlysis. Tylor & Frncis, London Europen Environment Agency (1990) CORINE-Lnd Cover dt Ewing R (1994) Chrcteristics, cuses nd effects of sprwl: literture review. Environ Urbn Issues 21:1 15

19 2 The Structure nd Form of Urbn Settlements 31 Glster G, Hnson R, Rtcliffe MR, Wolmn H, Colemn S, Freihge J (2001) Wrestling sprwl to the ground: defining nd mesuring n elusive concept. Hous Policy Debte 12: Getis A, Ord JK (1996) Locl sptil sttistics: n overview. In: Longley PA, Btty M (eds) Sptil nlysis: modeling in GIS environment. Geoinformtion Interntionl, Cmbridge, pp Hrris RJ, Longley PA (2000) New dt nd pproches for urbn nlysis: models of residentil densities. Trns GIS 4: Hrvey EO, Clrk W (1965) The nture nd economics of urbn sprwl. Lnd Econ 41:1 9 Hyden D (2004) A field guide to urbn sprwl. Norton, New York Mesev V (ed) (2003) Remote sensed cities. Tylor & Frncis, London Peiser R (2001) Decomposing urbn sprwl. Town Plnn Rev 72: Pendll R (1999) Do lnd use controls cuse sprwl? Environ Plnn B 26: Rzin E, Rosentrub M (2000) Are frgmenttion nd sprwl interlinked? North Americn evidence. Urbn Affirs Rev 35: Smith S (2004) Post processing of irborne scnning dt (LIDAR). Unpublished Ph.D. thesis, CASA, University College London, London Smith S, Hollnd D, Longley PA (2005) Quntifying interpoltion errors in urbn irborne lser scnning models. Geogr Anl 37: Trnsporttion Reserch Bord (1998) The costs of sprwl revisited. Ntionl Reserch Council, Ntionl Acdemy Press, Wshington, DC

20