Unit 6

Cities and Urban Land-Use Patterns and Processes: the one-page sheet

6.1 The Origin and Influences of Urbanization

Cities first grew where farming produced a food surplus, mostly in river valleys. Site (the physical place) explains where a city starts; situation (its links to other places) explains much of how it grows, and situation can change. Urbanization, a rising share of people in cities, is driven by transport, communication, population growth, migration, development and policy.

A city is a large, dense settlement where most people work in jobs other than farming. Urbanization is the growth in the share of people who live in cities.
The first cities grew in river valleys such as the Tigris and Euphrates in Mesopotamia (Iraq), the Nile in Egypt, the Indus in Pakistan and the Huang He in China, and separately in Mesoamerica. A food surplus came first.
Site is the place itself: the land, water and shape of the ground. Situation is where it sits among other places. A site rarely changes unless people reshape the land; a situation changes when routes change.
Urbanization is driven by transport, communication, population growth, migration, economic development and government policy, often several at once.

some people can stop farming and become builders, traders, priests and rulers the first cities form, often on a site that is easy to defend and near water its situation draws trade and jobs, so it keeps growing people move from rural areas to cities, and the urban share of the population rises: urbanization

city: A large, dense settlement where most people earn a living from work other than farming, such as trade, government and services.
urbanization: The process by which a growing share of a population lives in cities, through migration to cities and their growth.

6.2 Cities Across the World

Megacities (10 million or more) and metacities (20 million or more) are multiplying, mostly in Asia and Africa. In the United States and other high-income countries, cities spread outward instead: suburbanization and sprawl produced edge cities (suburban job centers), boomburbs (fast-growing suburban cities) and exurbs (commuter homes among farms).

A megacity has 10 million people or more; a metacity has 20 million or more. These are conventions, and a city's count depends on where its edge is drawn.
Most megacities are in Asia (19 of 33 in 2025, UN DESA), and most new ones are growing in lower- and middle-income countries.
Suburbanization is the movement of people and jobs from central cities to the surrounding suburbs. Low-density spread across the land is urban sprawl.
An edge city is a suburban center of offices and stores with more jobs than homes. An exurb is a rural-looking area beyond the suburbs where commuters live. A boomburb is a fast-growing suburb that has become a large city of its own.

their largest cities pass 10 million people and become megacities families moved from central cities to suburbs: suburbanization the metro area sprawls, and most trips need a car edge cities grow where highways meet, and boomburbs and exurbs grow beyond them

megacity: An urban area with 10 million people or more. The threshold is a convention, and a city's count depends on where its edge is drawn.
metacity: An urban area with 20 million people or more, a convention UN-Habitat used for the largest megacities.
suburbanization: The movement of people, jobs and stores from a central city to the lower-density suburbs around it.
urban sprawl: The spread of a city at low density over a large area, often across farmland, with homes, shops and jobs far apart.
edge city: A suburban center of offices, malls and hotels, usually near highway junctions, with more jobs than residents.
exurb: A rural-looking area beyond the suburbs, with homes on large lots, whose residents mostly commute into the metro area.
boomburb: A suburb that has grown very fast into a large city of its own, but is not the main city of its metro area.

6.3 Cities and Globalization

World cities sit at the top of the urban hierarchy because they host the headquarters, banks, law firms, media and international bodies that steer the world economy. They form a network linked by flows of money, information and people, and decisions made in them spread down the hierarchy and out to places at every scale.

A world city (also called a global city) is a city whose firms, banks and organizations make decisions that reach across the world. Its power comes from its links, not its population.
The urban hierarchy ranks cities by the size of the area they serve and control: a few world cities at the top, then major regional cities, national cities, regional cities and small towns.
World cities form a network. In the 2024 GaWC study, London and New York were the two most connected cities, based on the offices of finance, law, consulting, accounting and advertising firms.
Global decisions made in world cities have local effects elsewhere: a choice in London can open or close a factory in Viet Nam.

their headquarters and top offices cluster in a few big cities they become world cities at the top of the urban hierarchy ideas, investment and fashions spread from them down the hierarchy and out across the world housing costs rise, and the gap between high-wage and low-wage workers widens inside them

world city: A city whose companies, banks and organizations make decisions that reach across the world economy; also called a global city. Its rank comes from its functions and links, not its population.
urban hierarchy: A ranking of cities by the size of the area they serve and control, from a few world cities at the top to many small towns at the base.

6.4 The Size and Distribution of Cities

The rank-size rule predicts a smooth ladder of city sizes; a primate city breaks it, usually because a capital or colonial port gathered power and money. The gravity model predicts more interaction between big, close places. Central place theory explains the spacing of settlements from threshold and range. All four are models that fit some countries better than others.

The rank-size rule: the city of rank n has about 1/n the population of the largest city. A primate city is a largest city far bigger than the second (often more than twice as big) that dominates its country.
The gravity model: interaction between two places rises with their populations and falls with the square of the distance between them: $\frac{P_1 \times P_2}{d^2}$ .
Central place theory (Christaller, 1933): settlements are market centers. Threshold is the fewest buyers a seller needs; range is how far people will travel for a good. Market areas are drawn as hexagons.
Each is a model with assumptions: a flat, even plain, equal travel in every direction, shoppers going to the nearest place. Real borders, landforms, cars and online shopping bend them.

it can only open where enough people live within reach high-order goods gather in a few large places; low-order goods are sold in many small ones a pattern of a few large central places and many small ones forms, a hierarchy of market areas it grows far larger than the next city and becomes a primate city, breaking the rank-size pattern

rank-size rule: A model in which the city of rank n in a country has about 1/n the population of the largest city, giving a smooth ladder of city sizes.
primate city: A country's largest city when it is far larger than the second city (often more than twice as large) and dominates the country's economy, government and culture.
gravity model: A model that predicts interaction between two places grows with their populations and falls with the square of the distance between them.
central place theory: Christaller's model of settlements as market centers serving the areas around them, with a few large, widely spaced places and many small, close ones.
range (central place): In central place theory, the greatest distance people will travel to buy a good or service.
threshold (central place): In central place theory, the fewest customers a seller needs to stay in business.

6.5 The Internal Structure of Cities

Urban models describe how land use is arranged inside cities. North American models move from one center (concentric zone, sector) to many (multiple nuclei, galactic city) as cars spread. Latin American, Southeast Asian and African city models show how colonial history and fast growth create other patterns, such as squatter settlements at the edge. Each fits some cities and fails in others.

The central business district (CBD) is the commercial heart of a city, with the highest land values. Bid-rent theory explains why: the center is the most accessible place.
North American models: concentric zone (rings), sector (wedges along transport lines), multiple nuclei (several centers) and galactic city (old downtown plus edge cities along a ring highway).
Regional models: the Latin American city (a wealthy spine, rings that get poorer outward, squatter settlements at the edge), the Southeast Asian city (focused on the old port) and the African city (several CBDs).
Every model is simplified from certain cities at a certain time. Judge its fit: say where it works, where it fails, and why.

businesses outbid homes for it, so the central business district (CBD) has the tallest buildings and highest land values uses sort into zones, as in the concentric zone model zones stretch into wedges along them, as in the sector model several centers form, as in the multiple nuclei and galactic city models

central business district: The central business district: the commercial core of a city, with offices, stores and the highest land values.
concentric zone model: Burgess's 1925 model, based on Chicago, in which a city grows outward in rings around the CBD, from a zone in transition to a commuter zone.
sector model: Hoyt's 1939 model in which land uses form wedges that spread outward from the CBD along transport lines, with high-rent wedges continuing in one direction.
multiple nuclei model: Harris and Ullman's 1945 model in which a city has several centers, such as a CBD, a port, a university and an industrial district, each drawing its own land uses.
galactic city model: A model of car-based US metro areas in which an old downtown is ringed by suburbs and edge cities spaced along a beltway; also called the peripheral model.
Latin American city model: A model of Latin American cities with a CBD by the main plaza, a wealthy commercial spine, rings that get poorer outward and squatter settlements at the edge.
Southeast Asian city model: A model of Southeast Asian cities centered on the old colonial port, with commercial, government and mixed zones, new suburbs and market gardens at the edge.
African city model: A model of African cities with three CBDs (colonial, traditional and market), ethnic neighborhoods, a mining or factory zone and informal settlements at the edge.
squatter settlement: Housing built by residents on land they do not legally own or rent, often lacking piped water, sewers and secure title; also called an informal settlement.

6.6 Density and Land Use

Housing and land use reflect culture, technology and the cycles of building and decline that every city goes through. Residential density is usually highest near the center and falls toward the edge. Zoning rules lock in density patterns, and infilling adds new buildings on empty lots inside the built-up area.

Residential density is the number of homes (or people) on a given area of land. High-density housing means apartments; low-density housing means detached houses on large lots.
Housing reflects culture (courtyard homes for family privacy in old Fez, Morocco; single-family houses with yards in many US suburbs) and technology (elevators and steel frames made towers possible; cars made low-density suburbs possible).
Zoning is a set of local laws that says what kind of building and land use is allowed on each piece of land. It shapes density for decades.
Land goes through cycles of development: building, aging, decline and rebuilding. Infilling is building on vacant or underused lots inside an area that is already built up.

builders put more homes on each lot, so residential density is highest near downtown cities grow up in some eras and spread out in others some areas allow apartments and stores, others allow only single houses, which locks in a density pattern later investors and cities may fill the gaps with new buildings: infilling

infilling: Building new homes or businesses on vacant or underused lots inside an area that is already built up, instead of on open land at the edge.
zoning: Local laws that divide a city into zones and set what may be built in each, such as homes, stores or factories, and how tall or dense.
residential density: The number of housing units or people on a given area of land; apartments give high density, detached houses on large lots give low density.

6.7 Infrastructure

Infrastructure is the network of transport, utilities, communications and public buildings that lets a place function. Where it is located and how good it is shape where firms invest, where people can live and how healthy and connected they are, so it shapes patterns of economic and social development at every scale.

Infrastructure is the set of basic systems a place needs to work: roads, rail, ports and airports; water, sewer and power; phone and internet networks; and public buildings such as schools and clinics.
Its location matters: firms and homes gather where it reaches, so new rail stations and highway exits pull growth toward them.
Its quality matters: frequent power cuts, unsafe water or crowded roads raise costs and harm health.
Infrastructure can help some people and harm others: a highway that speeds suburban commuters may cut an old neighborhood in two.

firms and families can locate there cheaply and safely land values, jobs and tax revenue rise in those districts residents spend more time and money on basics, and health and jobs suffer patterns of economic and social development inside the city become more unequal

6.8 Urban Sustainability

Urban sustainability policies try to meet a city's needs without wasting land, energy or money. Smart growth tools (mixed use, walkability, transit-oriented development, New Urbanism, greenbelts and growth boundaries, slow-growth caps) can cut sprawl and driving, but critics point to higher housing costs, possible segregation and loss of historic character.

Smart growth is a set of planning policies that steer growth into compact, walkable areas instead of sprawl. Tools include mixed-use development (homes, shops and offices together) and transit-oriented development (dense building around transit stations).
Walkability is how easy and safe it is to reach daily needs on foot. New Urbanism designs neighborhoods with walkable streets, porches, nearby shops and a mix of homes.
A greenbelt is a ring of protected open land around a city; an urban growth boundary is a line beyond which building is limited. Slow-growth cities cap how many new homes may be built each year.
Praise: less sprawl, less driving, more housing choice, livelier streets. Criticism: higher housing costs, possible de facto segregation, loss of historic character.

new homes and offices go into land already inside the city, so density rises more trips can be made on foot, by bike or by train, so car use and emissions fall land and home prices can rise, so lower-income families may be priced out some residents welcome shops and housing choices, while others feel the area loses its historic character

smart growth: Planning policies that steer new building into compact, walkable, connected areas near existing services and transit instead of spreading onto farmland.
New Urbanism: A design movement that builds neighborhoods like older towns, with walkable street grids, homes near the sidewalk, a town center and a mix of housing.
mixed-use development: Development that puts homes, shops and offices in the same building or block, such as apartments above stores.
transit-oriented development: Dense, mixed-use building within a short walk of a rail or rapid bus station, so people can live and work without a car.
greenbelt: A ring of protected farmland, parks and forest around a city where building is restricted; an urban growth boundary is a line beyond which building is limited.
walkability: How easy and safe it is to reach daily needs, such as shops, school and work, on foot.

6.9 Urban Data

Urban geographers study change with quantitative data (census and survey counts of people, housing, income and travel) and qualitative data (interviews, field observation and residents' narratives). Numbers show what changed and how much; qualitative data show why and what it means. Each has limits, so strong answers use both and name the scale of the data.

Quantitative data on cities come from censuses and surveys: population, age, income, rent, how people travel to work. Survey data come from asking a sample of people a fixed set of questions.
In the United States, the census counts everyone every 10 years (most recently in 2020); the American Community Survey asks a sample of households each year, so its figures are estimates with a margin of error.
Qualitative data on cities come from interviews, field studies, photos, mental maps and residents' stories. They show attitudes and reasons.
Every source has limits: numbers miss meaning; a few interviews may not represent everyone; data for a whole city can hide differences between its neighborhoods.

planners can see what changed and by how much in each neighborhood researchers add interviews, field observation and residents' stories they show meaning and causes but cannot show how common a view is a city can make decisions that fit both the trends and the people living through them

survey data: Information gathered by asking a sample of people the same set of questions, such as the American Community Survey; results are estimates with a margin of error.

6.10 Challenges of Urban Changes

US cities were shaped by redlining and blockbusting, which drained investment from some neighborhoods; by urban renewal, which cleared many of them; and by gentrification, which brings investment and displacement. Around the world, squatter settlements face insecure land rights and poor services, and pollution often falls hardest on poorer communities. Cities respond with inclusionary zoning, fair-lending laws, land titles, local food projects and regional planning.

Redlining is refusing loans, insurance or other services, or offering worse terms, because of a neighborhood's location. In US history it targeted mostly Black and immigrant neighborhoods. Blockbusting was agents scaring white owners into selling cheaply by claiming Black families were moving in, then reselling at high prices.
Urban renewal is government clearing and rebuilding of areas it judges run-down. Gentrification is higher-income people moving into a lower-income area and raising its property values. Both bring investment and both can displace residents.
Other challenges: housing costs, unequal access to services, crime, disamenity zones (the poorest, least-served areas), squatter settlements without secure land rights, and environmental injustice (pollution falling hardest on poor and minority communities).
Responses include inclusionary zoning (new buildings must include affordable homes), fair-lending laws, land titles for squatters, local food projects and regional cooperation across fragmented local governments.

owners cannot buy, repair or sell, so buildings decline land becomes cheap, and the city clears it (urban renewal) or investors buy it buildings are repaired and new shops open, but rents and taxes rise many renters are displaced, so cities respond with inclusionary zoning, rent help and land trusts

redlining: Refusing loans, insurance or other services, or offering worse terms, based on a property's location; in US history it was aimed mostly at Black and immigrant neighborhoods.
blockbusting: A practice in which real estate agents scared white owners into selling cheaply by claiming Black families were moving in, then resold the homes at higher prices; outlawed in the United States in 1968.
gentrification: The movement of higher-income residents and investment into a lower-income neighborhood, raising property values and often displacing long-time renters.
urban renewal: A government program that buys, clears and rebuilds areas judged to be run-down, often displacing the people who lived there.
disamenity zone: One of the poorest, least-served parts of a city, such as an area of abandoned buildings or of unsafe land where the newest arrivals settle.
inclusionary zoning: A zoning policy that requires or rewards developers for including homes priced for lower- and middle-income households in new buildings.
environmental injustice: The unequal burden of pollution and environmental harm on poor and minority communities.

6.11 Challenges of Urban Sustainability

Growing cities face sprawl, poor sanitation, air and water pollution, high energy use and climate risks such as heat and flooding. Their ecological footprints reach far beyond their limits. Cities respond by cleaning up and reusing brownfields, drawing growth boundaries, protecting farmland and planning across a whole metro area, and each response has trade-offs.

Urban sustainability challenges include sprawl, sanitation, climate change, air and water quality, and energy use.
A city's ecological footprint is the area of land and water needed to supply what its people use and to absorb their waste. Cities' footprints are far larger than their own area.
A brownfield is an abandoned or underused industrial or commercial site that may be polluted. Cleaning it up lets the city grow inward instead of outward.
Responses include regional planning across many local governments, brownfield cleanup, urban growth boundaries and farmland protection. Each has costs as well as benefits.

people drive farther, so fuel use, air pollution and greenhouse gases rise rain runs off fast, carrying oil and trash into rivers and raising flood risk untreated waste reaches water supplies, harming health growth goes onto land already in use, and the city's footprint on the land grows more slowly

ecological footprint: The area of productive land and water needed to supply what a population uses and to absorb its waste, usually far larger than the area the population lives on.
brownfield: An abandoned or underused industrial or commercial site, such as an old factory or rail yard, whose reuse is held back by real or suspected pollution.