The urban world at the dawn of the 21st century has assumed special importance for two principal reasons. First, the world's population has recently crossed the threshold from being more rural to being more urban. In absolute terms and according to UN estimates, this means that of the world's population of approximately 6.8 billion, approximately 3.5 billion people (or 51%) are living in urban settings. To put this notion in historical context, consider that 58 yrs. (years) earlier only 29% of the world population lived in cities. The projection for 2050 is 70%. Second, a dramatic change in the urban hierarchy is taking place as the large cities—variously termed global cities, world cities, megacities, and so on—are beginning to dominate the urban landscape. This entry first reviews the historical development of the urban world, from the earliest settlements in Mesopotamia to the present, and the types of explanations researchers have used to describe this process. Problems in measuring the degree of urbanization are then discussed, including the concept of urban degree (the level of a country's urban concentration, expressed in percentage at a point of time). Although urbanization is occurring around the globe, there are significant differences in this process; some of the global trends are noted here. The entry concludes with a look at the future of urbanization.
Along with urbanization, other changes are taking place concomitantly: The rural-urban and interurban mobility of population is accelerating, the traditional rural-urban dichotomy is blurring, and research and technological innovations in economic development and transportation—along with the relaxation of political-institutional barriers—are growing. Consequently, a diversified and unprecedented mix of urban phenomena, urbanization processes, and urban patterns in global and regional scales is emerging, giving rise to complex issues, problems, and prospects. The concentration of urban populations is manifested in many forms and functions—both historically, through cyclical changes (e.g., urbanization, de-urbanization, and re-urbanization), and spatially, from the monocentric, core-oriented settlements to the polycentric, peripherally focused patterns.
Urban fringe, urban cluster, urban sprawl, “rurban,” and extended urban areas are among the terms frequently used to identify and characterize the spatial patterns of the emerging urban landscapes. Urbanization is linked with social and demographic changes such as smaller family sizes, occupational specialization, and increased population densities. Ideally and typically, urbanization is tied with increasing wealth and improved quality of life. While an urbanizing world has the potential to impart extraordinary benefits—including an enhancement of the quality of life—to its citizens, it also faces significant problems that include the degradation of environment and a challenge to urban sustainability. Urbanists seek to analyze these diverse urban issues from a variety of perspectives and scales in order to understand the spatial processes and patterns.
Early urban settlements were small but iconic representations or symbols of civilization, extensively written about in a number of regional contexts. Even though the concentration of population in settlements can be traced historically, the evidence of urban origin—the where, when, and how of urban concentrations and their subsequent spread—remains uncertain. Scholarly disagreements on the genesis, traits, settlement patterns, and modes of dispersal of urbanization notwithstanding, we know that urbanization has been a nearly continual process throughout human history. The earliest cities, or urban settlements, first developed approximately 6,000 yrs. ago in Mesopotamia. These were followed by cities developing independently in the Nile Valley in Egypt, the Indus Valley in South Asia, the Yellow or Huang He River valley in China, parts of Africa, and Mesoamerica and South America over the next several millennia. These regions are widely cited as the early “urban hearths.”
Of the theories offered to explain urban origin, four broad theories—hydraulic, economic, military, and religious—provide the dominant views. Briefly, a surplus in agricultural production was a critical notion underlying the hydraulic theory, and the notion of cities as the locations for trade was central to the economic theory. In the military theory, the need for concentration was attributed to the communal defense, while the role of religious leaders in the organization and control of territories for ensuring the safety and security of community dwellers was the basis of the religious theory. Clearly these explanations are not mutually exclusive.
Historically, urbanization has been linked with the progress of society from agrarian to industrial. Most societies before the 16th century were only marginally urban, as the vast bulk of the populations consisted of peasants and farmers. The mode of agricultural production, extraction of natural resources, and trading activities of urban dwellers had distinctive geographical and locational advantages. Subsequently, the progress of the agrarian economy, increased trade in the 16th century, and the onset of the Industrial Revolution in the 18th century laid the foundation of large-scale urbanization. Cities grew in number and population and became interlinked in trade and commerce.
Urbanization as a global phenomenon accelerated markedly with the advent and expansion of European colonialism. This diffusion of urbanization may be broadly depicted in several phases: The earliest phase grew incrementally and most apparently in Latin America, subsequently appearing in South Asia, Southeast Asia, and Africa. Other parts of Asia, such as China, were affected too, though later and not to the same degree. This first phase, lasting until the mid 1800s, was rooted in city-based mercantile colonial activities. During this period, city growth occurred mostly in colonial trading centers.
A second, industrial colonial phase was evident from the mid 1800s through the 1920s. During this phase, urbanization was increasingly tied to the extraction of raw materials for industrial activities and for growing food consumed in the rapidly expanding industrial centers. States were more directly involved in territorial control of their colonies. Colonial urbanization became more complex and more pervasive. Cities grew rapidly, became denser and increasingly segregated, and came to bear the hallmarks of European colonial planning.
The emergence of diversified urban economies and the development of a variety of transportation modes in the 19th century provided the stimulus for urbanization to accelerate, while distinctive patterns of urbanization became evident during the second half of the 20th century, especially during the post-World War II period. Several factors can be attributed to this distinctive pattern. First, many of the so-called less developed countries gained independence from colonial rule and initiated socioeconomic developmental planning emphasizing large-scale industrialization. Second, some of the more developed industrial countries shifted their industrial base from traditional manufacturing to a wide range of tertiary activities. This shift altered the location of activities by prompting regional redistributions of population within countries while spreading industries to new sites outside the core cities and countries. Third, the revolutions in finance, trade, and commercial activities involving both the developed and the developing countries, particularly during the past 25 yrs., gave rise to the process of globalization, which is intrinsically linked to the accelerated growth and development of many larger cities. One prominent outcome of the globalization process is seen in the emergence of the current global city or world city.
Throughout world history, urbanization, industrialization, and societal changes have been closely interrelated. Two key factors, broadly speaking, have shaped the pattern of urbanization over the centuries: the demographic (population base and growth rates) and the economic (resource base, growth rates, and development), making the socioeconomic development path key to understanding urbanization. This intricate relationship makes it imperative to understand, measure, and monitor urbanization, primarily by means of assessing the urban concentrations of population in space and over time.
In general, urbanization is described as the process of concentration of a population in space designated as urban—a process that encompasses the migration of populations from rural to urban areas, a natural increase in the urban population, and a reclassification of rural areas to urban. Although the idea of spatial concentrations of population might appear to be simple, it is well recognized that a variety of its correlates manifest themselves in urban space, reflecting the complexities of the process. Virtually all the countries of the world have designated their urban places or areas, although the conceptual definition of the term urban remains variable. Broadly, the following are among the key criteria that have general global acceptance:
A minimum threshold of population size, built-up area, or density
Occupational traits of the labor force (primarily nonagricultural)
Spatial structure and organizational pattern
In spite of the general agreement on the key criteria, the study of urbanization is fraught with two problems, namely, that the urban concept is not uniformly defined across the globe and that the data on the criteria for urbanization lack uniform definition, stringency, accuracy, or availability. These problems make it difficult to adequately assess and compare the urban status or patterns of individual countries or regions, not to mention the difficulties involving intracountry or cross-country comparability. Traditionally, easily computable demographic data, such as a minimum threshold of population size, are used for determining the urban status of a designated place. This simple approach reflects one of the many urban traits that arise out of population concentration. Wide variations in urban concentrations are apparent across nations, usually related to the countries’ levels of development and industrialization. In this respect, measurement of urbanization becomes a key indicator in assessing the developmental status.
The change in the degree of urbanization (urban degree) can be measured in two ways: (1) urban growth—the difference in the level over a period of time and (2) the relative difference between urban and rural growth rates. If the urban growth rate exceeds the rural growth rate over a specified time period, an urbanizing process sets in, indicating change in the societal status of the country. The measure of concentration and change in a population, as noted in its urban degree, growth, and urban-rural differentials, is related to a host of underlying demographics (e.g., birth rates, death rates), economic (e.g., migration of labor force), and/or administrative (e.g., urban designation policy) factors.
The difficulty in generalizing about global urbanization primarily arises from the complex geographies of countries and regions. First, the geographic patterns of the level of urbanization vary substantially across the globe. By world region, the world's most urbanized areas are North America (the United States and Canada; 81%), Latin America (78%), Europe (72%), and Oceania (71%). Less urbanized areas are Africa (39%) and Asia (41%). Given their demographic magnitude, it is wise to single out the urbanization levels of China (47%) and India (29%). Notable countries at the extremes are Singapore (100%) and Uganda (13%). Next, the pattern of change across the developed and less developed regions, both in the number of urban populations and in the rate of urbanization, are noticeably uneven (Figure 1). Irrespective of their level of urbanization, during the 25 yrs. following World War II, the urban population steadily increased in both the developed countries and the less developed countries. However, during the next 25 yrs. (1975-2000) both the size and the growth rates of the urban population in the less developed countries significantly exceeded the same in the more developed countries.
The urban structure, depicting the proportion of population distributed in a variety of size groups of places within given geographical and/or administrative territorial boundaries, can indicate important attributes of spatial development as observed in many regions in less developed countries. During the period from 1975 to 2000 (Table 1), the pattern of change in three selected hierarchical size groups of urban population showed a steady rise in the number of urban settlements in the smallest (>1 million population) size group, while they declined in their share of the total urban population. For the intermediate (1-5 million) and the largest (>5 million) size groups, the number of settlements increased, while their proportion of total urban population either increased or remained steady during these years. The structural patterns did not show much variation between the more developed countries and the less developed countries. However, compared with the smallest (<1 million) size group, a rather dramatic growth in the number of settlements for the two larger-size classes in the less developed countries depicts significant changes in the urban system (Table 1).
The emergence of megacities—those with 10 million or more people—marks a milestone in the 20th-century urbanization of the less developed countries. Out of a total of 19, there were only 5 megacities in the developed regions in 2007 (Table 2). It is estimated that by the year 2025, only one more city will be added to the megacity list in the developed region, while the rest, accounting for nearly 80% of the total number of cities, will be in the less developed countries. Over the past two decades, megacities in the less developed countries have experienced significant growth. Some, such as Dhaka in Bangladesh and New Delhi in India, recorded a huge increase of 11.3 million and 11.5 million people, respectively, during the period from 1975 to 2007. The average population of the world's largest 100 cities now stands at more than 7 million, compared with only 700,000 in 1900. The observed trends are attributed, broadly, to the forces generated from within (e.g., development policies) and/or outside (e.g., economic globalization) the more developed countries and the less developed countries.
Urbanization is a universal process. No matter how its evolutionary path is traced or interpreted, the certainty of its steady pace can hardly be disputed. Much social progress and development and economic prosperities are derived from urbanization. The continuity of the pattern of growth and pace, however, also clearly indicated the vulnerability of the urban environment. The basic issue for the future, then, is simple: How should the urban world grow?
While discussing the pros and cons of urbanization in the context of the global urban revolution, there are two major differing views on the state of urbanization. The “urban optimists” are motivated by the notion that the societal benefits of urbanization generate an overall improvement in the quality of life of the individuals as well as in the developmental levels of nations. The “urban pessimists,” on the other hand, worry about the adverse effects of urbanization, especially in the context of the developing countries, where socioeconomic unrest and urban pathologies such as poverty and slums continue to plague society. People across the globe perhaps see their individual and collective urban futures somewhere along the continuum.
To optimize the benefits of urbanization for societal development while minimizing, or at least coping with, its adverse consequences, it is imperative that research be focused on the global, national, and regional or local scales to understand the divergent paths of the complex urbanization phenomenon. In charting the future course of urbanization, the needs and wants of the people for a desirable urban living environment in a variety of contexts must be incorporated. Just as it is essential that the stakeholders—the citizens, the private and the public bodies—participate in envisioning the urban culture for shaping the future, it is equally crucial to collect, store, and distribute accurate and comparable urban data for ongoing research that would serve as the foundation for effective planning strategies and policies.
Counterurbanization, Gentrification, Rural-Urban Migration, Suburbs and Suburbanization, Uneven Development, Urban and Regional Development, Urban and Regional Planning, Urban Environmental Studies, Urban Geography, Urban Hierarchy, Urban Land Use, Urban Planning and Geography, Urban Policy, Urban Spatial Structure, Urban Sprawl, Urban Sustainability, Urban Underclass, World Cities, Zoning
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