GaWC Project 34

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Quantifying the World City Network: An advanced exploratory research to further specify, measure and analyse the relationship between world cities and contemporary globalization

Funded by: FWO (Fonds voor Wetenschappelijk Onderzoek)

Fonds voor Wetenschappelijk Onderzoek

Grant holders: Frank Witlox (Project Leader), Ben Derudder and Piet Saey (Ghent University)

Partners: Geert Wets (Limburgs Universitair Centrum)
Peter Taylor (Loughborough University)

Research associate: Anne Bunneghem


The contemporary study of world cities started with Friedmann and Wolff’s (1982) identification of 'command centers' to control and articulate the 'new international division of labour' being created by multinational corporations. For the first time, a shift from an international to a global economy, characterized by increasingly integrated global networks of production and services, was recognized whereby world cities played an important role (Amin and Thrift, 1992). These key world cities, as asserted in Friedmann’s seminal World City Hypothesis (1986, p. 71), were used by global capital as ‘basing points’ in the spatial organization and articulation of production and markets, and the resulting linkages make it possible to arrange them into a complex spatial hierarchy.

The lack of theoretical agreement and associated dearth of suitable data on the defining characteristics of world cities has resulted in a series of ad hoc taxonomies (e.g. Knox, 1995), often limited to the highest ranks of the hierarchy (e.g. Sassen, 1991; Abu-Lughod, 1995).

While it is obvious that cities like London and New York are world cities, there has hardly been a consensus as to the status of less significant cities in this context (Beaverstock et al., 1999). In other words, the highest ranks of the world city network may very well stand out, but the absence of more detailed taxonomies of cities below the leading cities in the world economy is a problem. As a consequence, somewhat vague discourses on patterns of global competence in the outer reaches of the world city network have dominated the debates. For instance, some authors have reified the lower ranks of the hierarchy as ‘sub-global cities’ (e.g. Daly and Stimson, 1992; O'Connor and Stimson, 1995), while this is particularly problematic given the pervasive nature of globalization. In a special issue of Urban Geography (Knox, 1996), it has been indicated that these ‘medium cities’ have just as much need to respond to globalization trends as their larger neighbours.

One of the major consequences of the problems pertaining to a description of Friedmann’s ‘complex spatial hierarchy’ is thus that the lower rungs of this transnational urban hierarchy have remained unassessed due to a lack of suitable data and a proper methodological approach. It was Taylor (2001, p. 192) who first tried to shed some new light on the problem by indicating that world cities constitute a complex network rather than a simple hierarchical structure, and that in order to measure this world city network specific data and exploratory research techniques were needed (see also Taylor et al., 2002a, 2002b). Taking advantage of the work already been done, the prime purpose of this project is to go one step further in specifying, measuring and quantifying this world city network. Hence, three main avenues for research, i.e. (i) specification, (ii) measurement, and (iii) quantification of the world city network, will be pursued whereby the main emphasis will be placed upon the investigation of the third research question.


Specifying the world city network entails an analysis of two closely entwined research questions: first, a formal specification of world cities as constituting a network rather than a hierarchy, and second, an analysis of the actors that create and systain this network. First, conceiving world cities as constituting a network entails that their specification relates to the identification of ‘cities in global matrices’ (Smith and Timberlake, 1995). Related discourses focus on a 'global network of cities' (King, 1990, p. 12), a 'transnational urban system' (Sassen, 1994, p. 47), 'functional world city system' (Lo and Yeung, 1998, p. 10), or a ‘global urban network’ (Short and Kim, 1999, p. 38). The implications of these various different conceptualisations have never been fully discussed in the world city literature. This is a first specification aspect that will be analysed in this project.

Second, this network specification directs our attention to the actors that create and sustain the world city network. Drawing on Sassen’s (1991, 1994, 1995) work on the role (and in particular the location strategies) of advanced producer services in world city formation, this research project will treat world cities as global service centres, i.e. locales where advanced producer services are concentrated for servicing their global corporate clients (see for a further rationale). The resulting world city network will thus be formally specified as an inter-locking three-level structure: a network level (the world city network), a nodal level (world cities), and a subnodal level (firms providing the advanced producer services). It is at the latter level that world city network formation takes place. Through their attempts to provide a seamless service to their clients across the world, financial and business service firms have created global networks of offices in cities around the world. Each office network represents a firm’s global strategy for dispensing its services, it is an outcome of location decision making at the scale of the world-economy. The world city network is therefore defined as the aggregate of the many service firms pursuing a global location strategy (Taylor, 2001). It is global service firms that ‘inter-lock’ world cities into a network of global service centres: they are the prime producers of the contemporary world city network. As such, their corporate behaviour determines the outcome and also the future of the world city network and needs to be further studied.


Having specified the world city network, the construction of a set of data that can be used to measure inter-city relations is an important next step. Drawing on the specification outlined in the first section of this proposal, a theoretically grounded endeavour of data acquisition (both at city and company level) has already been undertaken by Taylor et al. (2002a). The resulting model can be formally represented by a matrix Vij defined by n cities times m firms where vij is the ‘service value’ of city i to firm j. Service value (i.e. a score from 0 to 5) is the importance of a city to a firm’s office network which depends upon the size (e.g. number of practitioners) and extra-locational functions (e.g. regional headquarters) of an office or offices in a city. Thus every column denotes a firm’s global strategy and every row describes each city’s mix of services. This allows for two types of study: a focus upon the columns will inform our knowledge of firms; a focus on the rows will inform our knowledge of cities. Here, our analysis primarily concentrates on the latter, understanding the configuration of cities within the data. At present, 316 cities have been selected, whereas the total number of firms equals 100.

The fact that there already exists a data set that can be used as starting point for our analysis is an essential asset. It does however also raise some important addition questions which we aim to answer in this project. Apart from a thoroug validation of the data, i.e. ana analysis of the way they have been collected (via internet) and the process of standardization, three main other issues will be addressed in this project: (i) the question of the sensitivity of the data (how robust are the data?), (ii) the question of dynamics (how to deal with changing corporate business behaviour?), and (iii) the question of improving and extending the data (in terms of additional cities, additional firms and sectors, and more complicated definitions of service values). Answering these three questions will no doubt further improve the measurement of the world city network.


Once the network of world cities has been further specified and measured, it needs to be quantified. This is the main task of the research project. Taking advantage of previous research done by the current project team (Taylor and Walker, 2001; Taylor et al., 2002b; Derudder and Witlox, 2002; Wets & Witlox, 2001) we would like to test the usefulness of a series of data analysis techniques (e.g. fuzzy clustering analysis, data mining techniques) on their ability to further quantify the world city network.

At present our input data is a 316 x 100 matrix Vij where vij ranges from 0 to 5. One of the most popular data analysis techniques for studying large data matrices is cluster analysis. Applied to the matrix produced here, a traditional clustering algorithm would compute mutually exclusive clusters of cities, based on the various service values for the world cities. However, this classical approach towards cluster analysis is fraught with various sources of problems (Derudder and Witlox, 2002). First, the world city network does not exhibit a simple hierarchical urban structure. Plotting either sizes of cities (Ettlinger and Archer, 1987) or their connectivities (Taylor et al., 2002a) against their rankings produces neither a ranked size nor a primate distribution as conventionally found in studies of ‘national urban systems’ (e.g. Berry and Horton, 1970, chapter 3 for a discussion, and Bourne, 1975, chapter II for examples). Neither form of hierarchy is found at the global scale, instead the curve takes the form of the inverse of the primate city pattern. This is empirical support for the argument made in Taylor (2001) that world cities constitute a complex network rather than a simple hierarchical structure. Although the two first cities ranks may stand out (London and New York), the rest of the curve shows that this is not a ‘double-primate’ city pattern (Tayler et al., 2002a). As a consequence, clear-cut patterns, as provided by a traditional clustering algorithm, are unlikely to provide a sensitive specification of patterns in this complex network. Second, mixing hierarchical, regional and functional patterns augment this inherent complexity. There may or may not be hierarchical patterns within the spatial organisation of individual firms at the global scale (depending on their particular strategies), but when aggregated, the result is a complex network exhibiting multiple hierarchical and regional patterns. An exploration of the world city network should therefore include an assessment of intertwining hierarchical and regional patterns of global competence. Again, it is unlikely that a crisp cluster allocation will provide a sensitive specification of these scrambling patterns. Third, the main reason for the limitation of previous assessments to the upper and medium rungs of the hierarchy lays in the fact that the outer reaches of the world city network are to be classified based on sparse data, yielding vagueness in any classification based on this data. As a result, minor shifts in the sparse data may yield completely different outcomes, and mutually exclusive clusters are therefore unlikely to be unbiased. Hence, the possibilities offered by applying fuzzy clustering techniques may solve this problem.

A second important methodological avenue is the use of data mining techniques. Due to the complexity of the data matrix it becomes extremely difficult to interpret these data effectively such that new knowledge can be extracted. Because of this, a strong need exists to visualise this data matrix appropriately and subsequently, automatically extract knowledge from it. In the past several statistical techniques and SQL queries were used for this purpose. Currently, however, there is growing evidence that in many cases these techniques can be complemented by techniques originating from the field of machine learning. These so-called data mining techniques focus on extracting (semi-) automatically new knowledge from the data through association rules (Fayyad et al., 1996).

Because the exisiting data are collected per city, which combines services values for a series of advanced producer services, we can use these data to investigate world city associations. The empirical investigation of the data consists of the following stages. In the first phase, we investigate the properties of the different candidate measures of association. We define a city-producer service association as the joint occurrence of producer services characteristics. Several measures are available including Yule, association rules, and association coefficients. In the second phase, we perform a preliminary analysis to obtain a list of important world city associations using the association-rule technique (Agrawal et al., 1993). This data-mining technique enables us to find ‘important’ associations in a very efficient way at various hierarchical levels. It will result in a significant reduction of the number of associations. For retained associations, we can investigate their stability over time, and investigate their responsiveness to changing corporate business behaviour (change in service values) by calculating association elasticities, which quantify the sensitivity of the association between world city categories to changes in corporate behaviour and spatial changes. In the third phase, we perform an in-depth analysis for each of the important associations. More specifically, we investigate the impact of service values on the extent of association between ‘important’ world city-category pairs. This will bring with it new insight in the formation of the world city network.


The end-product of our research proposal is an analysis of the world city network at a level of geographical detail never before attempted. The current research project will try to enhance insight into globalization through the depiction of a new and detailed geography of the world city network. We will not limit ‘globalization forces’ to just a limited number of ‘global cities’, but will incorporate a very large number of cities into a single global urban analysis, resulting in a good empirical understanding of the contemporary world city network.

In summary, the results of this research project will enable us to draw conclusions about:

  1. the conceptualisation and scaling of the world city network;
  2. the role of service firms as driving force in the globalisation process;
  3. the validation and extension of the input data matrix;
  4. the suitability of different types of data analysis techniques (fuzzy clustering, data mining, others) to quantify the complex world city network.


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Agrawal, R., Imielinski, T. & Swami, A. (1993) Mining Association Rules Between Sets of Items in Large Databases. Proceedings of the ACM SIGMOD Conference, pp. 207-216.

Amin A. & Thrift N. (1992) Neo-Marshallian nodes in global networks. International Journal of Urban and Regional Research. Vol. 16, pp. 571-587.

Beaverstock J.V., Smith R.G. & Taylor, P.J. (1999) A roster of world cities. Cities. Vol. 16, pp. 445-458.

Bourne, L.S. (1975) Urban Systems. Oxford (UK), Clarendon.

Daly M.T. & Stimson R.J. (1992) Sydney: Australia's gateway and financial capital. In: Blakely E.J. & Stimson R.J. (Eds) New Cities of the Pacific Rim. Berkeley (CA), Institute for Urban and Regional Development (University of California).

Derudder, B. & F. Witlox (2002) "Classification techniques in complex spatial databases: On the assessment of a network of world cities". Solstice: An Electronic Journal of Geography and Mathematics. Ann Arbor, University of Michigan, Vol. XIII (1), 32 blz.

Ettlinger N. & Archer J.C. (1987) City-size distributions and the world urban system in the twentieth century. Environment and Planning A. Vol. 19, pp. 1161-1174.

Fayyad, U.M., Piatetsky-Shapiro, G. & Smyth, P. (1996) From data mining to knowledge discovery: An overview. In: Fayyad, U.M., Piatetsky-Shapiro, G., Smyth, P. & Uthurusamy, R. (Eds.) Advances in Knowledge Discovery and Data Mining. Menlo Park (CA), MIT Press, pp. 1-34.

Friedmann J. & Wolff G. (1982) World city formation: an agenda for research and action. International Journal of Urban and Regional Research. Vol. 6, pp. 309-344.

Friedmann J. (1986) The world city hypothesis. Development and Change. Vol. 17, pp. 69-83.

King A.D. (1990) Global Cities: Post-Imperialism and the Internationalism of London. London, Routledge.

Knox P.L. (1995) World Cities in a World-System. In: Knox P.L. & Taylor P.J. (Eds) World Cities in a World-System. Cambridge (UK). Cambridge University Press, pp. 3-20.

Knox P.L. (1996) Globalization and Urban Change. Urban Geography. Vol. 17, pp. 115-117.

Lo F. & Yeung Y. (1998) Globalization and the World of Large Cities. Tokyo, UNU Press.

O'Connor K. & Stimson R.J. (1995) The Economic Role of Cities: Economic Change and City Development, Australia 1971-1991. Canberra, AGPS.

Sassen S. (1991) The Global City. Princeton (NJ), Princeton University Press.

Sassen S. (1994) Cities in a World Economy. Thousand Oaks (CA), Pine Forge Press.

Sassen S. (1995) On concentration and centrality in the global city. In: Knox P.L. & Taylor P.J. (Eds) World Cities in a World-System. Cambridge (UK), Cambridge University Press, pp. 63-78.

Short J.R., Kim Y., Kuus M. & Wells H. (1996) The dirty little secret of world cities research - data problems in comparative analysis. International Journal of Urban and Regional Research. Vol. 20, pp. 697-719.

Short J.R. & Kim Y-H (1999) Globalization and the City. New York, Longman.

Smith D.A. & Timberlake M. (1995) Cities in Global Matrices: Toward Mapping the World-System’s City System. In: Knox P.L. & Taylor P.J. (Eds) World Cities in a World-System. Cambridge (UK), Cambridge University Press, pp. 79-97.

Taylor P.J. (2001) Specification of the World City Network, Geographical Analysis. Vol. 33, pp. 181-194.

Taylor P.J. & Walker D.R.F. (2001) World cities: a first multivariate analysis of their service complexes. Urban Studies. Vol. 38, pp. 23-47.

Taylor P.J., Catalano G. & Walker D.R.F. (2002a) Measurement of the world city network. Urban Studies. Vol. 39, pp. 2367-2376.

Taylor P.J., Catalano G. & Walker D.R.F. (2002b) Exploratory analysis of the world city network. Urban Studies. Vol. 39, pp. 2377-2394.

Wets, G. & F. Witlox (2001) "Decision-making using fuzzy decision tables: theory and illustration". Belgium Journal of Operations Research, Statistics and Computer Science (JORBEL). Vol. 41 (3).

For results of this project, see GaWC Research Bulletins 196 and 249.