Urbanization and Cities What is a city? Only recently in the history of their species have people gathered in the densely populated and highly structured settlements we call cities. The first cities were established about 5,000 years ago, but it has only been in the last 200 years—with the advent and spread of industrialization and with the global population rising at an exponential rate—that cities have grown significantly in size and number. At the start of the 20th century only about one person in ten lived in a city, but today the proportion of urban and rural dwellers is approximately equal. By 2025 nearly two-thirds of the world's population will live in urban areas. Many people are ambivalent about cities, believing that they embody the best and worst aspects of civilization. On the one hand, the diversity of peoples and activities encourages innovation and creativity, which in turn create opportunities that attract still more people. On the other, problems of overcrowding, crime, poverty, and pollution may be severe. Cities, therefore, have come to reflect the hopes and fears of the modern world. The definition of an urban area, as distinguished from a rural area, differs from country to country. Whilst most demographers would accept that cities are large, densely populated, built-up areas, there is little agreement about how to define "urban" using objective measures. Most countries use a combination of criteria: typically population size, population density, and the extent of the built-up area. However, few countries use the same measurements. In the United States, for example, census takers regard urban areas as those with at least 2,500 people, but in the United Kingdom the figure is 1,000. Such differences make it difficult to draw comparisons between countries. In economic terms, all cities are similar in the variety of functions, such as manufacturing, retailing, and services that they provide. These functions are the economic base of a city generating employment and wealth. The larger a city is, the more numerous and highly specialized its functions are likely to be. By contrast, smaller cities and towns have fewer functions, which tend to be of a more general nature. In the field of health care, for example, clinics are found in a wide range of places, but specialized teaching hospitals tend to be located only in larger cities. There are several reasons for the concentration of a variety of functions in cities. The large pool of urban residents sustains the demand for specialized functions. The clustering, or agglomeration, of related activities saves time and money. Cities are also linked to other settlements by a transport network, making it easy for people from outside the city to travel there to access the goods and services the city provides. Cities can also be defined in terms of their social composition. Cities are characteristically places with a large, dense, and heterogeneous, or varied, population. Some people would argue that these qualities give rise to a distinctive urban way of life. In the past, when cities were clearly demarcated from the surrounding countryside and communications were more limited than they are today, this urban way of life was confined to the cities themselves. As cities have expanded and mass communications have disseminated urban values, however, it becomes increasingly difficult to identify a uniquely urban life style. The Process of Urbanization A country is said to become more urbanized as its cities grow in number, its urban populations increase in size, and the proportion of its population living in urban areas rises. The degree of urbanization varies across the world but generally reflects the wealth of individual countries. The rich, industrialized countries tend to be the most highly urbanized. In the Netherlands, for example, 89 per cent of the population is urban, compared to only 13 per cent in Ethiopia, a much poorer country. In recent history, the degree of urbanization has been relatively low in Africa and Asia compared to Europe and North America. However, as a result of large-scale migration from rural areas and a natural increase in the urban populations themselves, the populations of cities in the developing world have been growing rapidly. The population of Cairo, for example, has trebled in the last 40 years, and more than half of Africa's people are expected to be living in cities by 2020. Similarly, the urban share of the population in China has risen from about one in five in 1960 to nearly half today. One of the most noticeable features of urban growth in the 20th century has been the rapid increase in the number of very large cities. Before 1800, cities with more than a million inhabitants were rare. Since then, however, the number of such cities has risen steadily. In 1900 there were at least 13 cities with more than a million inhabitants, and by 1950 the number had grown to 68. By 2000 there will be at least 250 cities of more than a million—many of which will be in Asia, especially in India and China. Even a city of a few million people is dwarfed by the urban giants with populations exceeding 10 million. According to various estimates, there may be 20 or more of these gigantic metropolitan areas already. Most are in Asia: Tokyo, Seoul, Osaka, Shanghai, Mumbai (Bombay), Beijing, Calcutta, Jakarta, Tianjin, Karachi, Delhi, and Manila. The other giants are New York, Sao Paulo, Mexico City, Los Angeles, Moscow, Buenos Aires, Rio de Janeiro, and Cairo. In coming years, explosive growth in cities of the developing world such as Lagos and Santa Fe de Bogotá will almost certainly propel them into this group. By the year 2020, several cities are expected to have populations of more than 20 million. Such large concentrations of people pose immense environmental problems. In Mexico City, for example, one-quarter of the population has no access to running water, and one in five houses is not connected to the sewerage system. Located in a valley, the city suffers so badly from air pollution from motor vehicles that the city center must periodically be closed to traffic. Mexico City's problems are replicated in most other large cities in the developing world, and to a lesser degree in the large cities of industrialized countries as well. Another characteristic of the growth of urban giants is the coalescence of once separate cities into a continuous built-up area. As transport improves, people are able to commute longer distances, and cities have sprawled outwards. Although each city within the built-up area maintains its own government, in physical terms the individual cities blend into one. The term megalopolis (Greek for "great city") was coined to describe the nearly continuous urban area that stretches about 800 kilometers (500 miles) along the Atlantic Coast of the northeastern United States from Boston to Providence, Hartford, New York City, Newark, Philadelphia, and Baltimore to Washington, D.C. The term has since been extended to other areas in which urban sprawl links once separate cities, such as Randstad in the Netherlands, the Ruhr Valley in Germany, and the Tokyo-Yokohama-Kawasaki region in Japan. The Location of Cities The location of a city often depends on its original function, which is usually related to defence, trade, resources, administration, or religion. Strategic needs were very important in the past, particularly when the control of movements through an area was essential. In Afghanistan, for instance, Kabul grew up on the site that controls traffic over the Khyber Pass, one of the principal routes across the mountains of the Hindu Kush. Trade is a more peaceful force that drives the location of cities. Good communications and transport links are vital if trading cities are to flourish. For example, Singapore controls the Strait of Malacca, one of the main shipping routes between the ports of East Asia and those to the west. The existence of scarce resources is another important factor in the location of cities. Johannesburg is an example of a city that has developed close to valuable resources—in this case the staggeringly rich goldfields of South Africa. In like fashion, Kiruna and Gallivare in the cold north of Sweden lie at the heart of plentiful deposits of iron ore. Cities established as administrative centers, such as Madrid in Spain and Santiago in Chile, often occupy a central position, so as to offer more or less equal access to all parts of the country. The site of Washington, D.C. was selected for the capital as the midpoint of the original 13 United States from south to north. Finally, a number of cities originated on sacred sites. Mecca has developed largely because it was the birthplace of Mohammed, the founder of Islam. Millions of people from throughout the Islamic world flock there each year on a pilgrimage known as the hajj. The text is based on "Urbanization and Cities", http://www.pacificislandtravel.com/nature_gallery/urbanization.htm.