Origin, Distribution, and Systems of Cities
The Origin and Influence of Urbanization
The permanently inhabited portion of the Earth’s surface is referred to by the classical Greeks as the ecumene. This area encompasses a variety of community types and population densities. As humans transitioned into permanent locations, classifications for settlements emerged: rural areas (farms and villages) characterized by low concentrations of people; urban areas (cities) characterized by high concentrations of people; and suburbs, which are primarily residential areas located near cities. A settlement is defined as a place with a permanent human population. The first agricultural settlements appeared approximately years ago. Before this, humans survived through hunting and gathering, necessitating temporary or movable shelters. Early permanent settlements were small enough that inhabitants could subsist on surrounding fields. Over time, these agricultural settlements developed into the first true urban settlements, or cities, through three primary drivers: the presence of an agricultural surplus, the rise of social stratification and a leadership class (the urban elite), and the beginning of job specialization.
Food surpluses were made possible through the development of irrigation, farming techniques, and the domestication of plants and animals. These advancements allowed more people to live together in a single location. A ruling class emerged to control accumulated products and community members. Job specialization occurred because not every resident was needed for food production; some became specialists in tool making, weapons, or art, while others served as accountants or religious leaders, forming the first service sector. Consequently, cities became economic centers focused on services, manufacturing, and trade. Urbanization is the ongoing process of developing towns and cities, which also involves studying the causes and effects of existing city growth. A region is described as urbanized if cities are present. The "percent urban" is a common statistic indicating the proportion of a population living in cities and towns compared to rural areas. Currently, more than of the world’s population lives in cities. Demographers estimate this will rise to by 2030 and nearly by 2050, with most growth occurring in less-developed countries (LDCs) within the world's periphery and semiperiphery. While urbanization can be positive, it presents overwhelming challenges if a city is unprepared for rapid growth.
Site and Situation in Urban Development
The location where a city develops is defined by two geographical concepts: site and situation. Site describes the immediate location's characteristics, such as physical features, climate, labor force, and human structures. Situation refers to the location of a place relative to its surroundings and its connectivity to other places—examples include being near a gold mine, on a coast, or near a railroad. The site and situation of a city directly influence its function. Specialized city functions can include defense, religion, trade, education, finance, transportation, government, manufacturing, retirement, entertainment, or residential services. Larger cities, such as Boston or New York City, may have multiple functions. Historically, city-states consisted of an urban center and its surrounding territory/agricultural villages, functioning independently. Defense was a primary consideration for these city-states, and military leaders often evolved into kings. Urban hearths, areas where early city-states emerged, were typically defensible sites in river valleys with fertile soils. These include the Tigris-Euphrates Valley (Mesopotamia) in modern Iraq, the Nile River Valley and Delta in Egypt, the Indus River Valley in Pakistan, and the Huang-He floodplain in China. Other centers emerged in Mesoamerica (Mexico) and the Andean region of South America. Historic examples include Athens, Sparta, Corinth, and Renaissance-era Venice. Modern city-states include Monaco, Vatican City, and Singapore, though the latter two evolved from religious influence rather than agricultural settlements.
Defining Modern Cities and Metropolitan Areas
A city is generally defined as a nucleated or clustered settlement with a high concentration of people. An urban area includes a central city, suburbs, and land developed for commercial, industrial, or residential purposes. Legally, a city is a high-density area with territory inside officially recognized political boundaries. This legal definition is essential for taxing, providing services, and law enforcement. A metropolitan area (or metro area) is a collection of adjacent cities economically connected with high, continuous population density. In the United States, a Metropolitan Statistical Area (MSA) consists of a city of at least people, the county it resides in, and adjacent counties with high social and economic integration with the urban core. Micropolitan statistical areas are similar but focus on cities with a population between and . These designations define a city as a nodal region, or focal point. Urban physical characteristics, or morphology, include the built-up area (high concentration of structures), the outskirts (where built-up areas meet open space), and the urban border (the end of the continuously built-up area).
Social Characteristics and Communication Networks
Cities exhibit high social heterogeneity, meaning they possess a greater variety of people compared to rural areas, including diverse cultural interests, sexual orientations, languages, and professional pursuits. Large cities often have high percentages of foreign-born residents; for example, Miami, San Jose, Toronto, Vancouver, Sydney, and Melbourne have foreign-born populations of or more. This diversity attracts more diversity, as individuals with less common cultures seek counterparts in urban centers. Improvements in transportation and communication have furthered urban growth. Time-space compression, through transportation improvements, has allowed urban areas to expand. The Internet has enabled remote work, increasing the distance people can live from a city center. Cities are nodal regions requiring connectivity; new technologies diffuse hierarchically to large cities first. In 2020, U.S. News & World Report identified Singapore as the city with the best communication network, or the top "smart city."
Borchert’s Transportation Model of Urban Growth
Geographer John Borchert developed a model to describe urban growth based on transportation technology, divided into four epochs. The Sail-Wagon Epoch () prioritized water ports, as poor road conditions made long-distance land travel difficult. The Iron Horse Epoch () saw steam engines power boats to grow river cities and regional rail networks connect resources to industrial sites. The Steel Rail Epoch () was marked by transcontinental railways and the emergence of cities along interior rail lines. The Auto-Air-Amenity Epoch () utilized cars to allow cities to spread out and saw the emergence of airport hubs and increased city interconnection. While the model ends in 1970, recent trends include the expansion of mass transit, biking, and walking infrastructure. Internally, cities evolved from pedestrian cities to horse-and-buggy cities, then to streetcar suburbs (communities along rail lines creating a pinwheel shape), and finally to automobile-dominated sprawling landscapes facilitated by highways and the U.S. interstate system.
Population Growth, Migration, and Policy
Rural-to-urban migration is driven by push factors (population pressure, cultural tension, environmental strain, lack of opportunity) and pull factors (economic hope, cultural freedom, government services). The most rapid migration currently occurs in periphery and semiperiphery countries like China, India, and Brazil. In Brazil, millions move from the north and west to Sao Paulo and Rio de Janeiro, causing challenges like substandard housing and stressed infrastructure. In core countries, migration has shifted toward cities in the West and South. In the United States, cities like Atlanta, Tampa, Charlotte, Denver, Dallas, and Phoenix have seen rapid growth due to perceived economic opportunity and quality of life. Governments use policies to encourage growth; for instance, Pittsburgh shifted from manufacturing to high-tech, attracting Google and Uber. China’s 2014 New Urbanization Plan designated the eastern coast for development, investing in cities like Shenzhen to create a global financial center and its own Silicon Valley.
Suburbanization and New Land Use Forms
Suburbanization is the process of people moving from cities to residential areas on the outskirts. In post-WWII North America, this was driven by economic expansion, car culture, and the Federal Housing Administration (FHA) providing mortgage loans for single-family housing. Racial tension also fueled "White flight" as African Americans moved North. Sprawl refers to the rapid horizontal expansion of a city, often caused by lower land costs and weak planning laws. Leap-frog development occurs when developers build beyond the city's periphery. Atlanta covers over for people, whereas Mexico City covers only for over people. New land-use forms include boomburbs—rapidly growing communities (over growth per decade) with over people that are not the largest city in their metro area (e.g., Mesa, AZ; Plano, TX; Riverside, CA). Edge cities are economic nodes in the periphery with office buildings and retail but few residences. Counter-urbanization or deurbanization involves residents leaving cities for exurbs—prosperous residential districts beyond the suburbs. Reurbanization describes suburbanites moving back into the city.
Megacities, Metacities, and Megalopolises
Megacities have populations exceeding . Metacities (or hypercities) are continuous urban areas with over people or networks of cities grown into an interconnected system. Tokyo is the world’s largest metacity with over people; New York City is tenth with over . An emerging metacity near Shenzhen is predicted to hit by 2050. A megalopolis is a chain of connected cities. The "Bos-Wash Corridor" (Boston to Washington, DC) includes nearly people and is a conurbation—an uninterrupted urban area. Other megalopolises exist in California (San Diego to San Francisco) and Japan (Tokyo to Yokohama). In 2020, 15 of the 20 largest urban areas were in semiperiphery or periphery countries.
World Cities and Urban Hierarchy
World cities (global cities) like New York, London, Tokyo, and Paris exert influence far beyond national boundaries as media hubs and financial centers. The top 10 world cities in 2020 by the Global Power City Index were: (1) London, (2) New York City, (3) Tokyo, (4) Paris, (5) Singapore, (6) Amsterdam, (7) Berlin, (8) Seoul, (9) Hong Kong, and (10) Shanghai. The urban hierarchy ranks cities by influence or population. Nodal cities (e.g., Denver, Phoenix, Minneapolis) are regional command centers with transnational corporate offices. Other cities specialize in functions: Austin (government), Las Vegas (entertainment), Elkhart (manufacturing), and Norfolk (military).
Rank-Size Rule and Primate Cities
The rank-size rule states that the largest city in a region will be approximately the size of the largest city. This distribution is characteristic of well-developed regions with federal governments. It implies a variety of services: higher-order services (expensive, rarely used, e.g., specialized research hospitals, major sports teams) and lower-order services (cheap, daily use, e.g., gas stations). The rule is seen in the U.S., Canada, Australia, and India. Primacy occurs when the largest city is more than twice the size of the next largest city. A primate city (e.g., London or Mexico City) is disproportionately powerful and common in unitary governments. In the UK, London () is much larger than Manchester (). In Mexico, Mexico City () dwarfs Guadalajara ().
Interaction Models: Gravity and Central Place Theory
The gravity model predicts that larger and closer places have more interaction (flows of workers, shoppers, etc.) than smaller, distant places. Its formula assumes no barriers, though political, physical, or cultural barriers do exist. Tourist and religious sites like Orlando, Las Vegas, Jerusalem, and Mecca can distort this model. Walter Christaller’s Central Place Theory (1933) explains city distribution based on consumer behavior. A central place is where people receive services. Christaller used hexagonal hinterlands to represent market areas because hexagons stack without overlap or gaps. The threshold is the minimum population needed for a service to be profitable (e.g., low for convenience stores, high for symphony orchestras). Range is the distance people are willing to travel for a service (e.g., small for toothpaste, large for heart transplants).
Questions & Discussion
1. Describe TWO ways that you think U.S. cities will change over the next 20 years. One prediction is the continued relocation of families into enclaves inspired by new urbanist designs, which offer walkable streets and local markets. Another is the expansion of edge cities and exurbs as self-driving cars and technology reduce the friction of distance and the need for central commuting.
2. Describe TWO challenges that megacities in Asia and Africa could face in the future. Megacities face the risk of exceeding their carrying capacity, leading to a deterioration in the standard of living. Additionally, dense concentrations of people may increase the impact of deadly epidemics, environmental pollution, and civil unrest.
3. Based on the data for these ten urban areas, which region of the world has the most megacities? Asia has the most megacities, with cities like Tokyo, New Delhi, Shanghai, Mumbai, Osaka, and Beijing appearing on the list.
4. Seven of the ten largest urban areas are in periphery and semiperiphery countries. Explain two factors that contributed to the growth of megacities in these countries. High birth rates within these countries and increased rural-to-urban migration driven by the hope for economic opportunities and government services are the two primary factors.