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.

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.

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.

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.

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.

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.

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.

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.

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.

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.