More than half the world’s population now lives in cities whose growth, both in numbers and surface area, is aggravating the problems of housing, traffic, pollution, energy consumption and social inequality. International organizations, NGOs and civil societies are calling for public policy changes in order to effect a transition to cities with low carbon emissions—cities that are more compact, more resource-efficient, and socially fair.

More than half the world’s population now lives in cities (55% in 2015 as against 30% in 1950 and probably 68% in 2050). This global urbanization means that cities are becoming ever denser, more sprawling and interconnected, the focus of both the innovations and pathologies of contemporary societies. Megacities are on the increase: 513 urban areas now have over a million inhabitants compared with only 16 in 1900 and none in the early nineteenth century. Five of these have more than 20 million inhabitants (Tokyo, Delhi, Shanghai, Mexico City, Sao Paolo).

Networks of cities

The great urban areas of the world form the architecture of the globalization process: they are both its decision-making centers and the hubs of physical networks. A dual process combines an ever-increasing dispersal of production activities thanks to the development of mobility, both physical (transport) and non-physical (telecommunications), with an over-concentration of innovation in cities (economies of scale and especially density of interaction).

Top 150 urban areas by population and GDP, 2014-2015

Sources: European Commission, JRC , Global Human Se t tlemen t , ht tp://ghsl.jrc; Global Metro Monitor 2014,

Comment: A comparison of two maps showing the 150 largest urban areas in the world reveals very strong distortions between population and wealth. On the one hand, some urban agglomerations of between 10 and 20 million inhabitants have a high GDP (New York, Los Angeles, London, Paris), and on the other there are very many, especially in Asia, which have an extremely large population and low or very low GDP. We should remember that the total GDP of an urban area sometimes conceals very considerable gaps in wealth between social groups and/or neighborhoods.

Ideas about cities are neither stable nor shared, and statistical sources use different definitions. During the 1960s, the megalopolis of the east coast of the United States was described as a conurbation concentrating capital, authority, and power (Jean Gottmann). By the late 1980s, there were three megalopolises in the world: the east coast of the United States, Tokyo-Osaka-Kobe in Japan and the European backbone stretching from London to Milan (Roger Brunet). In the late 1990s, the concept of world megalopolitan archipelago appeared (Olivier Dollfus), to describe all the great cities where command and innovation activities were concentrated. A city’s hierarchical position in the global urban system can be defined by its degree of connectivity of all types (informational, intellectual, banking and transport networks), but this analysis of hierarchy has now given way to the study of a vast complex network (Jacques Lévy).

Territorialization of inequality

Urban population growth and the continuing rural exodus toward cities explain the speed of urbanization and create a demand for housing, infrastructures and services which many cities are unable to fulfill.

Top 15 urban areas, 2030

Source: United Nations , Population Division, World Urbanization Prospects: The 2014 Revision, 

Comment: According to UN forecasts, by 2030 all 15 of the largest urban areas in the world will have close to or more than 20 million inhabitants, 7 will have between 20 and 25, 4 will have around 30 and 2 will have more than 35 (Delhi and Tokyo). However, these figures have resulted from a variety of changes over the past 80 years: very rapid in the case of Asian and African cities, but slower in New York and Japan. Urban areas in the poorest countries are growing fastest.

This pressure is stronger in the cities of the South, where the exodus of the poorest permanently sustains shantytowns (or slums), made up of precarious dwellings on the edge of or even inside cities, in areas that are unbuildable, unfit for habitation, and dangerous.

Shanty towns and other types of informal habitat, 2014 

Source: United Nations, Sustainable Development Goals Indicators,

Comment: The map showing the population living in shanty towns and other informal dwellings is particularly mixed. As part of the urban population (the colored areas), the level is over 40% in most African countries, and exceeds 90% in South Sudan, the Central African Republic, and Sudan. In terms of numbers (proportional circles), the highly populated emerging countries (China, India, Brazil) show a large number of people living in shanty towns, whereas their proportion of the urban population is lower than in Africa.

With no rights of ownership, the very poor who live there have no access to drinking water or sanitation. According to the 2015 UN-Habitat statistics, at least 881 million pe live in overcrowded, informally-built housing where they are subject to socio-spatial exclusion. While between 2000 and 2014, the share of the urban population in Southern countries who live in shantytowns declined (from 39% to 30%), the numbers in absolute terms continue to grow, reflecting very diverse situations according to place and time. In some cases, city officials, having first attempted to make these sites invisible (surrounding them with high walls), and then to raze them to the ground (they simply spring up elsewhere), have finally laid on a minimum level of services, and sometimes legalized them or provided materials for upgrading the buildings. In other cases, the inhabitants are left to their own devices, more or less separated into communities supported by NGOs, and subject to the violence of the informal economy or organized crime. Despite being cut off geographically and socially, these shantytowns are not completely removed from the official city since they provide it with domestic labor, odd jobs, and street trade, at the cost of commuting over very long distances.

In contrast to this residential segregation suffered by default are forms of territorialization chosen by the rich. They may involve the gentrification of former down-at-heel working-class districts in the town center, whose inhabitants have been driven out, or the creation of exclusive residential quarters sheltering gated communities. First developed in the United States from the 1970s onward on the peripheries of towns, they are now very common in emerging countries and in the South, contributing to the extension of the urban sprawl.

Reinventing the city?

This dual growth of cities, in terms of both people and space occupied, has led to an increase in daily commutes, pollution (accounting for three-quarters of global greenhouse gases), and consumption of raw materials and energy in amounts that can no longer be sustained.

Extension of urban sprawl in selected cities, 1975-2015

Source: European Commission, Joint Research Centre (JRC), “GHS Settlement grid following the REGIO model 2014 in application to GHSL Landsat and CIESIN GPW v4-multitemporal (1975-1990-2000-2015)”.

Comment: The extension of urban sprawl in the seven examples selected reveals very different relationships between the most densely populated urbanized area (vertical city) and its horizontal extensions (geographical) which commonly encroach on rural space (houses or shanty towns). Some structures are polynuclear, connected by densely populated axes (Pakistan, Vietnam), while others, especially the Hong Kong/Shenzhen/Guangzhou/Macao urban area, have very high densities within a perimeter of over 150 kilometers in diameter.

Since the late 1970s, successive international conferences have encouraged changes in public policies: these involve a transition toward low carbon emissions and more compact cities which manage resources carefully and are socially fair (1976 Vancouver Declaration, 1992 Rio Conference and Agenda 21, 1996 Istanbul Summit, and Habitat III in Quito). City networks (the 80 cities of the C40 Cities Climate Leadership Group), smart cities, eco-neighborhoods, slow cities or experiments with urban agriculture are all signs of a growing awareness, and changes are being proposed in the areas of transport, waste management, energy, water, and construction, but these often leave aside questions of equality and social inclusion.

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