AP Human Geography Unit 6 Review: Cities and Urban Land-Use

Cities originate where site and situation make settlement and growth possible. Site is the physical character of a place, such as a defensible hilltop, fertile floodplain, or natural harbor. Situation is a place's connectivity to other places, such as being at a river confluence or along a trade route. Once established, cities grow because of changes in transportation, population growth, rural-to-urban migration, economic development, and government policy.

• Site: The physical characteristics of a location, such as terrain, water access, or natural resources, that make it suitable for settlement.
• Situation: A city's location relative to surrounding places and its connections through trade routes, transportation, or communication networks.
• Suburbanization: The movement of people and economic activity from city centers to surrounding suburban areas, driven by transportation improvements and government policies like highway construction.
• Industrialization: The shift to factory-based manufacturing that concentrated workers in cities and accelerated urban growth in the 19th and 20th centuries.

Urbanization produces different outcomes depending on where it occurs. Megacities exceed 10 million people and are increasingly found in periphery and semiperiphery countries such as Lagos, Dhaka, and Mumbai. Metacities exceed 20 million. In wealthier countries, suburbanization and decentralization have created edge cities, exurbs, and boomburbs. These new forms bring challenges including automobile dependence, sprawl, and uneven service provision.

• Megacity: An urban area with more than 10 million people, increasingly concentrated in the Global South.
• Edge Cities: Large suburban nodes with significant office, retail, and employment space that developed outside traditional city centers, such as Tysons Corner, Virginia.
• Suburban Sprawl: Low-density, automobile-dependent expansion of residential and commercial development into previously undeveloped land at the urban fringe.
• Exurban Area: A low-density area beyond the suburbs where residents commute to the city but live in a more rural setting.

World cities, also called global cities, sit at the top of the global urban hierarchy and serve as command-and-control centers for the global economy. Cities like New York, London, and Tokyo concentrate advanced producer services, transnational corporation headquarters, and financial markets. They are connected to each other and to lower-order cities through transportation networks, digital infrastructure, and trade flows, allowing them to shape and mediate global economic and cultural processes.

• Global City: A city that functions as a major node in the global economy, concentrating finance, corporate headquarters, and advanced services. Examples include New York, London, and Tokyo.
• Urban Hierarchy: The ranking of cities by size, function, and influence, from small towns to regional centers to global cities.
• Time-Space Compression: The way transportation and communication technology reduces the effective distance between places, enabling cities to maintain global connections.

Four concepts explain how cities are sized and distributed within a country or region. The rank-size rule predicts that the second-largest city will be half the population of the largest, the third will be one-third, and so on. A primate city dominates its country disproportionately, often holding more than twice the population of the next largest city. Christaller's central place theory explains how cities are spaced based on the threshold and range of services they provide. The gravity model predicts that interaction between two cities increases with population size and decreases with distance.

• Primate City: A country's largest city that is disproportionately larger and more influential than all other cities in that country, such as Paris in France or Bangkok in Thailand.
• Central Place Theory: Christaller's model explaining that settlements are distributed in a hierarchy based on the threshold population needed to support a service and the range customers will travel to reach it.
• Gravity Model: A model predicting that interaction between two places is proportional to their populations and inversely proportional to the distance between them.
• Market Area: The surrounding region from which a central place draws customers for its goods and services, also called a hinterland.

Several models describe how land use is arranged inside a city. The Burgess concentric-zone model places the CBD at the center, surrounded by rings of transition, working-class housing, middle-class housing, and commuter zones. The Hoyt sector model argues that land uses extend outward in wedges along transportation corridors. The Harris and Ullman multiple-nuclei model recognizes that cities develop around several specialized centers rather than one CBD. The galactic city model describes car-dependent cities where edge cities orbit a weakened downtown. Bid-rent theory explains that land values fall with distance from the CBD, shaping which users locate where. Regional models for Latin America, Southeast Asia, and Africa reflect how colonial history, informal settlements, and port-based development produce different spatial patterns.

• Burgess Concentric Zone Model: A model showing cities growing outward in concentric rings from the CBD, with each ring representing a different land use and socioeconomic group.
• Sector Model: Hoyt's model in which land uses extend outward from the CBD in wedge-shaped sectors along transportation routes rather than in uniform rings.
• Multiple Nuclei Model: Harris and Ullman's model showing cities organized around several specialized activity centers rather than a single CBD.
• Bid-Rent Theory: The principle that land values and the willingness to pay for land decrease as distance from the CBD increases, determining which land uses locate where.
• Galactic City Model: A model describing decentralized cities where edge cities and suburban nodes orbit a weakened central core, connected by highways rather than transit.

Residential density ranges from low-density single-family homes in suburbs to high-density apartment towers near city centers. These patterns reflect a city's culture, technology, and development history. Infill development adds housing on vacant lots within existing urban areas rather than expanding outward. Infrastructure, including roads, transit, water, sewer, and utilities, directly shapes where economic and social development occurs. Infrastructure decisions reflect political power: historically, redlining denied investment to minority neighborhoods, and highway construction displaced urban communities. The quality and location of transit, water, and sanitation infrastructure still produce unequal spatial outcomes today.

• Built Environment: The human-made physical surroundings of a city, including buildings, roads, parks, and utilities, which reflect social values and economic priorities.
• Urban Infrastructure: The physical systems a city depends on, including transportation, water supply, sewage, and energy networks, whose location and quality shape economic and social development.
• Gentrification: The process by which higher-income residents move into lower-income urban neighborhoods, raising property values and often displacing long-term residents.

Urban sustainability initiatives aim to reduce sprawl, improve walkability, and create more livable cities. Key tools include mixed land use, transit-oriented development, smart growth policies, New Urbanism, greenbelts, and slow-growth cities. Supporters argue these approaches reduce car dependence, improve housing diversity, and lower environmental impact. Critics point out that they can raise housing costs, create de facto segregation by income, and erase neighborhood character.

• New Urbanism: An urban design movement promoting walkable, mixed-use neighborhoods with human-scale design as an alternative to sprawl.
• Smart Growth: Planning policies that concentrate development in existing urban areas, preserve open space, and reduce automobile dependence through mixed uses and transit investment.
• Transit-oriented development: Compact, mixed-use development built around transit stations to reduce car dependence and encourage walkability.
• Green Belts: Designated open land around urban areas that limits outward sprawl and preserves agricultural and natural land.
• Mixed Land Use: Zoning that allows residential, commercial, and recreational uses in close proximity, reducing commute distances and supporting walkability.

Geographers use two types of data to study urban change. Quantitative data from sources like the census, American Community Survey, and census tracts provide measurable information about population size, composition, housing tenure, and migration flows. Qualitative data from field studies, oral histories, interviews, and participant observation capture how residents experience and perceive urban change. On the AP exam, you may be asked to read choropleth maps, population pyramids, or census tables and explain what they reveal about urban patterns.

• Census Data: Systematic demographic information collected by governments, used to track population size, composition, and housing characteristics in urban areas.
• Census Tract: A small statistical subdivision of a county used to collect and compare demographic data at the neighborhood level.
• Qualitative Data: Non-numeric information from interviews, field observations, and narratives that captures residents' experiences and attitudes toward urban change.
• Satellite Imagery: Remote sensing images used to detect land use change, urban expansion, and environmental conditions in cities.

As populations shift within cities, economic and social challenges intensify. Redlining was the practice of denying loans and investment to minority neighborhoods, producing lasting patterns of disinvestment. Blockbusting manipulated racial fears to profit from neighborhood transition. Zones of abandonment and disamenity zones emerge where disinvestment is severe. Squatter settlements form in cities where affordable housing is absent, especially in the Global South, creating land tenure conflicts. Responses include inclusionary zoning, community land trusts, and local food movements. Gentrification can revitalize neighborhoods but also displaces long-term residents. Fragmented government, where authority is split among city, county, and state agencies, makes coordinated responses difficult.

• Squatter Settlements: Informal housing built on land residents do not legally own, common in rapidly urbanizing cities in the Global South, often lacking basic services.
• Favelas: Informal settlements in Brazilian cities, characterized by self-built housing, limited infrastructure, and social marginalization.
• Food Deserts: Urban areas where residents lack convenient access to affordable, nutritious food, often linked to disinvestment in low-income neighborhoods.
• De Facto Segregation: Residential separation of groups that results from economic and social forces rather than explicit law, often reinforced by historical redlining and housing policy.

Cities face major sustainability challenges including suburban sprawl, inadequate sanitation, climate change, poor air and water quality, large ecological footprints, and high energy use. The urban heat island effect raises temperatures in dense built-up areas. Brownfields are contaminated former industrial sites that require remediation before reuse. Responses include regional planning, brownfield redevelopment, urban growth boundaries, and farmland protection policies. Each response has trade-offs: urban growth boundaries can limit sprawl but raise housing costs inside the boundary.

• Ecological Footprint: The total land and water area required to produce the resources a city consumes and absorb its waste, a measure of urban environmental impact.
• Brownfield: Previously developed, often contaminated land that is abandoned or underused and targeted for environmental remediation and redevelopment.
• Air Quality: The condition of urban air in terms of pollutant levels, affected by vehicle emissions, industry, and urban density, and a key sustainability challenge for cities.
• Sanitation: Systems for safe waste disposal and clean water provision, whose absence in informal settlements creates major public health and environmental challenges.