Multilevel comparison of large urban systems

For the first time the systems of cities in seven countries or regions among the largest in the world (China, India, Brazil, Europe, the Former Soviet Union (FSU), the United States and South Africa) are made comparable through the building of spatio-temporal standardised statistical databases. We first explain the concept of a generic evolutionary urban unit ("city") and its necessary adaptations to the information provided by each national statistical system. Second, the hierarchical structure and the urban growth process are compared at macro-scale for the seven countries with reference to Zipf's and Gibrat's model: in agreement with an evolutionary theory of urban systems, large similarities shape the hierarchical structure and growth processes in BRICS countries as well as in Europe and United States, despite their positions at different stages in the urban transition that explain some structural peculiarities. Third, the individual trajectories of some 10,000 cities are mapped at micro-scale following a cluster analysis of their evolution over the last fifty years. A few common principles extracted from the evolutionary theory of urban systems can explain the diversity of these trajectories, including a specific pattern in their geographical repartition in the Chinese case. We conclude that the observations at macro-level when summarized as stylised facts can help in designing simulation models of urban systems whereas the urban trajectories identified at micro-level are consistent enough for constituting the basis of plausible future population projections.Comment: 14 pages, 9 figures; Pumain, Denise, et al. "Multilevel comparison of large urban systems." Cybergeo: European Journal of Geography (2015

Empowering urban governance through urban science: Multi-scale dynamics of urban systems worldwide

Cities are facing many sustainability issues in the context of the current global interdependency characterized by an economic uncertainty coupled to climate changes, which challenge their local policies aiming to better conciliate reasonable growth with livable urban environment. The urban dynamic models developed by the so-called “urban science” can provide a useful foundation for more sustainable urban policies. It implies that their proposals have been validated by correct observations of the diversity of situations in the world. However, international comparisons of the evolution of cities often produce unclear results because national territorial frameworks are not always in strict correspondence with the dynamics of urban systems. We propose to provide various compositions of systems of cities in order to better take into account the dynamic networking of cities that go beyond regional and national territorial boundaries. Different models conceived for explaining city size and urban growth distributions enable the establishing of a correspondence between urban trajectories when observed at the level of cities and systems of cities. We test the validity and representativeness of several dynamic models of complex urban systems and their variations across regions of the world, at the macroscopic scale of systems of cities. The originality of the approach resides in the way it considers spatial interaction and evolutionary path dependence as major features in the general behavior of urban entities. The models studied include diverse and complementary processes, such as economic exchanges, diffusion of innovations, and physical network flows. Complex systems dynamics is in principle unpredictable, but contextualizing it regarding demographic, income, and resource components may help in minimizing the forecasting errors. We use, among others, a new unique source correlating population and built-up footprint at world scale: the Global Human Settlement built-up areas (GHS-BU). Following the methodology and results already obtained in the European GeoDiverCity project, including USA, Europe, and BRICS countries, we complete them with this new dataset at world scale and different models. This research helps in further empirical testing of the hypotheses of the evolutionary theory of urban systems and partially revising them. We also suggest research directions towards the coupling of these models into a multi-scale model of urban growth

Economic and demographic trends of municipalities in South Africa: An application of Zipf’s rule

There are vast differences among South African local municipalities, with a limited number of large municipalities (both in terms of population size and economic activity) and a seemingly disproportionate number of intermediate-sized and small municipalities. No clear systematic national approach has yet been adopted to assess the distribution of core variables at municipal level in South Africa. Zipf’s rule, which postulates a consistent regularity in the size and rank of cities, is applied to disaggregate the performance of South African local municipalities in terms of three variables (population, Gross Value Added and municipal income) within the overall national settlement pattern. The results indicate that the Zipf rank size rule distribution is applicable to municipal level population data in South Africa, but less so for Gross Value Added and municipal income. The position and relative changes of municipalities along the Zipf curve between 2001 and 2011 also provide plausible indications of potential future trajectories of the three variables classified according to the dominant settlement typology within each municipality. The results also emphasise the significant conceptual limitations when using only legally defined administrative municipal boundaries for analysis purposes without also considering economically functional boundaries.&nbsp

U.S. Metropolitan Spatial Structure and Employment Growth

This study explores the influence of US metropolitan spatial structure evolution on regional employment growth rate. The first part of this study investigates the evolution of US metropolitan spatial structures from 2000 to 2010. At the macro level, I categorized metropolitan areas (metros) into three groups (i.e., monocentric, polycentric, and coreless) based on the number of employment centers these metros had in 2000 and 2010. At the micro level, I sub-grouped the three macro spatial structure groups into micro-level clusters based on each metro’s rank of employment shares in five sub-metro locations: the main-center, sub-centers, non-center clusters, non-cluster urban areas, and rural areas. The results show that (1) among 361 US metros, over 80 percent of metros remained in their original macro spatial structure type, and (2) less than 10 percent of metros experienced employment decentralization. The second part of this study explores the influence of spatial structure evolution on regional growth rate. At the macro level, a series of two-sample t-tests showed that the group of monocentric metros that remained monocentric had no significant difference in employment growth rate from the group of monocentric metros that evolved to be polycentric. Conversely, the group of polycentric metros that remained polycentric had a higher employment growth rate than the group of polycentric metros that evolved to be monocentric. At the micro level, a regression analysis showed that the initial sub-centers’ employment share had a larger positive effect on regional employment growth rate than the initial main-center employment share, while the change in non-cluster urban areas’ employment share had a larger negative effect on regional employment growth rate than the change in the non-center clusters’ employment share. The main conclusions from this dissertation are that (1) employment decentralization from the main-center to sub-centers increases regional employment growth rate, whereas employment dispersion — employment migration from centers (i.e., main-center and sub-centers) to non-centers (i.e., non-center clusters, non-cluster urban areas, and rural areas) – decreases regional employment growth rate, and (2) metros’ macro and micro spatial structure types were relatively stable over the study period

The discourse, governance and configurations of polycentricity in transitional China: a case study of Tianjin

Polycentricity has been identified as a prominent feature of modern landscapes as well as a buzzword in spatial planning at a range of scales worldwide. Since the Reform and Opening-up Policy in 1978, major cities in China have experienced significant polycentric transition manifested by their new spatial policy framework and reshaped spatial structure. The polycentric transformation has provoked academics’ interests on structural and performance analysis in quantitative ways recently. However, little research investigates the nature of (re)formation and implementation of polycentric development policies in Chinese cities from a processual and critical perspective. This research interprets the underlying meanings and rationality of polycentric development strategy in planning discourse and explains how concrete centres within the polycentric system are created, governed and materialized to facilitate the implementation of polycentric policies in the special context of political system, spatial planning system and socio-economic conditions in China. Referring to existing literature of polycentricity and theories of urban space, this research develops a novel theoretical framework, which holds that polycentricity is produced by the articulation of state power, planning profession and produced space. The research is founded on an embedded case study of Tianjin based on empirical data derived from interviews with stakeholders and secondary data. Through a discourse analysis of four Tianjin City Master Plans, discourses of ‘polycentric urban settlements’, ‘functional polycentricity’, ‘polycentric growth nodes’ and ‘nested polycentricity’ are identified, which are deployed in different ways with variegated composition of spatial elements. Moreover, rather than being mere technocratic practice, the production and legitimation of distinct discourses is essentially an articulation of multi-scalar power involving various stakeholders, which is disguised and justified by the planning profession. The findings demonstrate that polycentricity is a malleable concept and its fluidity creates space to accommodate consensus or to allow the play of contested interests and policy experiments. Based on that, this research further selects centres in Tianjin Binhai New Area Core Zone, Wuqing District and Dongli District as embedded cases to explore how the polycentric development policy is implemented in practice. The empirical findings from local perspective show that these centres are created or formed according to different contexts and logics, and they are consolidated by employment of a portfolio of tools and instruments such as new planning and urban design, establishment of financial and development corporations, exclusive preferential policies, manipulation of public sector, land development and institutional innovation. Correspondingly, these centres have experienced distinct development trajectories and shown different spatial outcomes from the perspectives of urban form, functional composition, and spatial identity. It is suggested that significant gaps and contradictions exist between spatial visions and actual development, which poses challenges for sustainable development