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Unit 5: Human Population Dynamics // Section 6: Urbanization and Megacities


The year 2007 marked a new milestone for human population growth: for the first time, more people worldwide were living in cities than in rural areas (footnote 16). This trend is driven by several factors: people migrating from rural regions to cities; rural areas being reclassified as urban areas because of population growth; and urban populations growing and expanding their boundaries to incorporate land that was formerly classified as rural.

Urbanization is a predictable outcome of industrialization and the demographic transition. As nations shift to mechanized agriculture they can produce more food with less labor, so there are fewer work opportunities in rural areas. More investment flows into industry and service businesses, which concentrate in urban areas near customers and infrastructure such as highways and telecommunications services. As these sectors become the main arenas of economic activity, people who once might have spent their lives in rural areas move to cities in search of higher-paying work and better living standards.

Nearly all of the urban growth projected in this century will occur in developing countries. About three-quarters of the world's urban population lives in small or intermediate-sized cities, which have fewer than 1 million inhabitants or 1 to 5 million inhabitants, respectively (footnote 17). Most urban dwellers will continue to live in small and medium cities, but there also will be major growth in megacities (more than 10 million people) and metacities (more than 20 million people). In the 1950s only New York and Tokyo were large enough to qualify as megacities, but population experts project that six cities—São Paulo, Mexico City, Mumbai (formerly Bombay), Delhi, Dhaka, and Tokyo—will have topped the 20 million mark by 2015, with New York, Jakarta, and Lagos close behind (Fig. 14).

The world's largest cities in 2015

Figure 14. The world's largest cities in 2015
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Urban growth can contribute to sustainable development if it is managed effectively. Because cities concentrate economic activities and large numbers of people close together, the unit cost of providing basic infrastructure and services like piped water, roads, and sewage treatment is lower than in rural areas. Governments can make cities more efficient and livable by investing in public transportation systems and clean energy sources, and by planning ahead for growth so that they are able to provide basic services when populations expand.

But city life can also be dirty, unhealthy, and dangerous. Many people moving to cities, especially in the developing world, end up living in slums, just like earlier migrants to places like Manchester, England, and New York City's notorious Five Points slum in the 19th century. In 2007 the number of slum dwellers worldwide exceeds one billion, about one-third of all city residents, with more than 90 percent of slum dwellers residing in developing countries (footnote 18). Slums are a large and entrenched sector of many cities in the developing world. Some, like Brazil's favelas and South Africa's townships, have become sightseeing attractions for adventurous tourists.

Urban poverty can be as severe as rural poverty for people in slum neighborhoods who do not have access to the benefits of city life. The United Nations defines a slum as "a contiguous settlement where the inhabitants are characterized as having inadequate housing and basic services" such as drinking water and sanitation (footnote 19, Fig. 15). Slum dwellers typically live in crowded conditions without durable shelter or reliable access to safe drinking water or proper toilets. Many are not protected by tenants' rights, so they can easily be evicted or forced out and become homeless.

Shanty town in Manila beside Manila City Jail

Figure 15. Shanty town in Manila beside Manila City Jail
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Source: Courtesy Mike Gonzalez. Wikimedia Commons, GNU Free Documentation License.

People who live in slums have lower life expectancies than their neighbors in more affluent areas, and more slum residents are killed or sickened by environmental hazards like indoor air pollution and water-borne or water-related diseases. (For more about these threats, see Unit 6, "Risk, Exposure, and Health," and Unit 8, "Water Resources.") Ironically, many slum dwellers use less energy and resources and generate less waste than their upscale neighbors, but the poor live in dirtier areas and receive fewer resources and services, so they bear the burdens generated by higher-income consumers.

The scale of urban poverty, already a pressing issue in many developing countries, may become even worse, as most population growth in the 21st century will happen in cities. Ameliorating the conditions described above is essential for sustainable human development. Some countries, including Brazil, Cuba, Egypt, South Africa, Sri Lanka, Thailand, and Tunisia, have reduced or limited slum growth. These governments have made serious political commitments to upgrading slum neighborhoods, improving housing, giving more people access to clean water and sanitation, preventing more "informal" settlements (shanty neighborhoods), and investing in services like education and transportation that benefit poor communities. And after decades of focusing on rural communities, international aid organizations are paying increasing attention to urbanization.

"As I walk through the slums of Africa, I find it hard to witness children suffering under what can only be described as an urban penalty. I am astonished at how women manage to raise their families under such appalling circumstances, without water or a decent toilet. The promise of independence has given way to the harsh realities of urban living mainly because too many of us were ill prepared for our urban future. Many cities are confronting not only the problems of urban poverty, but the very worst of environmental pollution. From Banda Aceh to New Orleans, whole communities are being wiped out through no fault of the innocent victims."

Anna Tibaijuka, Executive Director, UN-HABITAT
(Worldwatch Institute, State of the World 2007: Our Urban Future)

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