Archives par mot-clé : Historical data bases

Singularities of urban systems in China and India

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We show for the first time comparable and exhaustive maps of cities for the largest two countries of the world[ref] Urban data bases have been built by Elfie Swerts from a variety of statistical and geographical sources according to a unified concept of urban agglomeration (continuously built up area). [/ref]. Around year 2000 there represent the precise location of about 11 000 cities above 10 000 inhabitants in China and 7000 in India, regrouping respectively 690 and 380 million of urban citizens (figure 1 and 2).

Two subcontinents of megacities and small towns

A major singularity common to both urban systems when compared to the rest of the world is the combination of huge metropolises with a high density of numerous smaller towns. Each country has at least three megacities above 10 million inhabitants (Shanghai, Beijing, Guanzhou, Delhi, Mumbai, Kolkata) and Shanghai and Delhi are even each above 20 million. No doubt that in the next decades more very large urban centers will emerge, many of the largest cities of the world will be found in Asia and even a handful of gigantic conurbations called “megalopolis”.

But the distinctive feature of these urban systems is their dense underlying pattern of small towns with population between 10 000 and 50 000 inhabitants, of which there are almost 9 000 in China and 5 400 in India. One third of the urban population of each country lives in these relatively small settlements (whereas the proportion is only 25% in Europe and 5% in the United States of America). These small settlements are disseminated in every region, according to a rather more regular spatial pattern in India compared to the asymmetry between sporadic Western and denser Eastern urbanization in China (due to environmental and historical factors).

Figure 1 Population sizes of urban agglomerations in China (year 2000)

Source : Swerts Chinacities, urban agglomerations above 10 000 inhabitants

Figure 2 Population sizes of urban agglomerations in India (year 2001)

Source : Swerts, Indiapolis and IndiaCensus, urban agglomerations above 10 000 inhabitants

Two different types of urban hierarchies

Even if both countries share with all other urban systems a strong differentiation of city sizes according to a Zipf’s distribution, China appears as an exception in the world. Although the share of urban population is higher in China (urbanization rate = 60% against 40% only in India) the index which measures the level of inequalities of city sizes in the system (that is the slope of the adjusted rank-size curve) is only 0.8 in China (against 0.9 in India) (figure 3). Moreover, while the general trend in India, in conformity with observations in other parts of the world is an increase of these urban size differences during the historical urbanization process, the slope has been decreasing during the last forty years in China. That can certainly be explained by the strength of urban and spatial planning policies in this country – even if an uncertainty remains about the identification of urban population because of the hukou system. It is also a demonstration that an evolution toward more and more hierarchy in urban systems is not as inescapable as it may appear from uncontrolled urban dynamics in most world countries.

Figure 3 Rank-size distributions of cities in China and India around 2000

Sources : China : Swerts, ChinaCities (2000), India : Swerts, Indiapolis (2001)

Elfie Swerts


Cities and Transport relations in South Africa over the long-term

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The aim of my study[ref]PhD project of Solène Baffi, under the supervision of Anne Bretagnolle, Olivier Ninot, Denise Pumain and Celine Vacchiani-Marcuzzo (founded by ERC GeoDiverCity) [/ref] is to understand the role of South African cities in the transport flux and networks, and how cities and transport are interacting, from colonization in the 17thuntil nowadays. If cities and transport interactions are a particularly interesting approach to understand the metropolisation process and the urban system building, the South African context makes it even more relevant. Indeed, South Africa is a young country and national transport networks such as the railway network, have been built while the urban system was formed.

Co-evolution of urban system and railway network in South Africa

The arrival of European settlers in 1652 to the Cape of Good Hope marked the beginning of South African modern history, in particular by initiating the urbanization process. Until then, no city, strictly speaking, existed yet (Coquery-Vidrovitch). The implementation of a settlement engaged the constitution of an urban system well connected with Europe, but not very well between cities (Vacchiani-Marcuzzo).

The discovery of the goldfields and diamond mines in the 1860’s overturned that system. In the heart of the mining region, Johannesburg faced a fast growth to become the biggest metropolis in the country. The emergence of this new centre deeply modified the urban structure by switching the country’s centre of gravity from the coast to the Witwatersrand. Indeed, the British Empire decided to experiment inner-city railways in Cape Town and Durban in the 1860’s. But given the mining revolution, the decision to extend it to the entire country was quickly made in order to dispatch the mining extractions from the Witwatersrand plateau to the shoreline before having them exported to Europe. Hence, in a bit less than 100 years, a 20 000 km railway network has been built.

The implementation of such a network whereas the urban system was formed enables us to talk about a co-evolution of urban system and transport network in South Africa. Citie’s growth has largely been influenced by their position on the railway network. Large cities benefitted from a better accessibility, which reinforced their centrality while small towns had to deal with the simplification of urban hierarchy. As in many other countries, we can notice the strong interaction between cities and transport and its effect on the process of cities selection, particularly reinforced  by the railway network in the South African example.

I started my research by focusing on the railway network given it seemed easier to start with an historical approach at the larger scale. To observe and study this co-evolution we decided to cross two databases created in Geographie-Cités. The first one, built in the research program Harmonie-Cités, gathers data about the evolution of South African cities (of more than 5 000 inhabitants) over almost a century. To create this database, South African censuses have been used. The second one, made up in the frame of Geodivercity research program, contains data about the railway network’s development in South Africa and has been built thanks to the SARH archives. By crossing these databases, we created maps over 60 years which show the concomitant evolution of the urban system and railway network.

Now, I intend to deepen my analysis and enlarge my focus to the implementation of transport in metropolitan areas on one hand, and the position of South Africa in global networks on the other.

Solène Baffi

Evolution and urban modeling: a complexity perspective on the Brazilian city system

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The project performed in this thesis, aiming at the knowledge of the Brazilian system of cities, sets out to demonstrate, within an historical and legal frame, the peculiarities of the history of urbanization in Brazil, a large and populous developing country that is widely considered to have completed an early urban transition.

Undertaking a research on this topics means, primarily, to handle with a problem of an apparent dearth of literature; even if is possible to find many works on Brazilian urbanization, above all in Portuguese language, only a few of these treats urbanization under the aegis of complex systems, as an adaptation process to changes arising from massive urbanization and from insertion in a global, hierarchized network of cities, in which, each metropolitan area is compelled to adapt its internal structure in response to demographic, economic and technical changes. Brazilian main centers will be considered as nodes of a hierarchized structure extending their influence over other agglomerations and territories.

A complexity perspective can provide a general appropriate context within which to understand the behavior of socio-economic systems, notably urban cities systems; computer based models will be associated to a geographical conception in order to analyze urban systems starting with geographical and historical data and trying to foresee their future dynamics through modeling.

By the means of an analysis of both geographical conception and computer-based conception of cities, we will try to set up a model that simulates the peculiarities and so the dynamics of cities and this will be explicitly done using the software Netlogo in order to realize a simulation of a cities system in Brazil. The testing done with our model will be also used to simulate the possible effects of climate changes on the future evolution of urbanization.

Cosmo Antonio Ignazzi

Is there a system of Russian cities? Generic properties and specificities in the description and modeling of Russian cities’ interactions

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In the context of GeoDiverCity, generic properties of city systems are looked for as stylized facts that apply to these particular objects over the world and over time. Examples of those properties lay in the hierarchy of city sizes (expressed by Zipf’s law), or the process of urban growth (as described by Gibrat in 1931). Using those regular patterns, modeling of the co-evolution of cities becomes possible and useful.

Russian cities oppose several obstacles to the observation of such regularities. The spatial limits of the system varies over time, which complicates  the choice of urban definition, and the collection of reliable data. Moreover, the historical object of Russia and the Soviet Union exhibits strong specificities related to its (supposed absolute) control over urban definition, development, interactions and inner organization. Our work aims at distinguishing the specific from the generic behavior of the Russian system of cities from the urban transition up to now, in order to model its evolution and propose possible projections with the help of Multi-Agent Models.

This project[ref] PhD project of Clémentine Cottineau, under the supervision of Denise Pumain (founded by University Paris 1 Panthéon-Sorbonne) [/ref] begins with the harmonization of urban definitions. Theoretical and data collection constraints led us to consider agglomerations of 10.000 inhabitants and more between 1840 and 2010. Agglomerations have been composed of administrative units which take part in the same built-up area in 2010. Since the boundary of the system is not obvious over the XIX and XXth centuries, its larger extension (the Former Soviet Union) is tested along with its present configuration (the Russian Federation).

Generic models (Zipf, Gibrat) are tested and compared with the results obtained in other geographical contexts. Europe, North America, South Africa, India, China and Brazil are represented in the research fields of GeoDiverCity, sharing the same principles of data harmonization, which helps us in the process of comparison. Other tools are used to explore and explain the specificities of the system of Russian cities (analysis of urban trajectories and financial links between cities with the ORBIS Database produced by Bureau van Dijk, 2010 and augmented by C. Rozenblat).

The characteristics of the Russian system learned from these studies, coupled with the experience accumulated within Géographie-Cités and GeoDiverCity will help modeling the system and simulating its possible futures.

Clémentine Cottineau

How to explore the future of cities? An evolutionary theory including urban dynamics and territorial history

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Within the framework of the GeoDiverCity programme we are attempting at modelling the future evolution of cities. As cities are very complex systems, any exact prediction is impossible. However, the exploration of plausible futures is possible, with an increasing approximation according to the length of time duration.

The theory behind our modelling is that cities have to be considered not as isolated entities but as interdependent systems being embedded in complex situations summarised by three major aspects:

–       the system of cities with which they have most of their interactions

–       the territory to which they belong

–       the historical period under consideration

Cities are depending on multiple interactions that occur with other cities in multiple networks for all kind of urban activities from local to global scales – that is why we always consider them as part of systems of cities; cities also are rooted in administrative and political territories that generate specific rules and constraints for their development, at local, regional, national and international levels; during the about ten thousands years period of their existence, the type of relations that cities have had with their environment has changed and despite its rather massive common features the urbanisation process has taken a wide range of variations in different parts of the world.

Analysing the evolution of systems of cities from large urban data bases, we suggest recognising that they share many common features but also exhibit a fundamental geo-diversity that is the expression of path dependence in their development. We can model the common dynamics of systems of cities from the interactions between cities, but for understanding and predicting their differentiated evolution we have to take into account their history.  This does not mean building a narrative of successive events but a careful selection of a few specific historical regimes that contextualise the development of systems of cities all over the world (including for instance quality of natural environment, steps of the demographic transition, or relative situation in innovation networks), as well as a restricted set of events that may have more specifically occurred during the history when trying to predict the evolution of any individual city.

Denise Pumain

The global hierarchy of port cities in 1890 based on steamer vessel traffic

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The enormous concentration of traffic upon a few large cities confirms the paramount importance of the Atlantic area (London, Liverpool, Cardiff, and New York) as well as of specific poles such as Hamburg and Buenos Aires, the latter being at the time a growing rival of European capitals. Other cities stand out less by their traffic than by their important share of steamer traffic, among which Antwerp, Bombay, Baltimore, and New Orleans. Asia is the region outside Europe hosting the largest number of cities specialized in steamer traffic.
For more information on data and further analyses (in French):
http://www.cnrs.fr/inshs/recherche/reseau-maritime-mondial.htm

César Ducruet

Flows of steamer vessels among world regions in 1890

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Based on the circulation of 4,772 merchant vessels on the period January-April 1890 (Source: Lloyd’s Weekly Shipping Index), the map reveals a trading system highly polarized by Europe and the United States – the main commercial centres at the time. The proportion of most modern vessels (steamers) in total traffic (including sailing vessels propelled by wind) concentrate on the most beneficial and frequent routes (Europe-USA) but also highlight the deployment of this recent innovation towards Asia and Africa in a context of reinforced colonial interests following the opening of the Suez canal (1869).

César Ducruet