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Cities Across
the World

Explore how urbanization, city models, and global networks shape where and how billions of people live.

AP Human Geography

What Is Urbanization?

Urbanization is the process by which an increasing proportion of a population comes to live in cities and metropolitan areas. It involves both the physical growth of urban areas and the migration of people from rural to urban settings.

Understanding urbanization is central to AP Human Geography because it connects to migration, economic development, cultural change, and environmental sustainability.

Key Urban Terms You Need to Know

Megacity
An urban area with a population exceeding 10 million people (e.g., Tokyo, Lagos, Mexico City).
Metacities
Urban agglomerations with over 20 million people, often formed when multiple metro areas merge.
Primate City
A city that is at least twice as large as the next largest city and dominates the nation's economy and culture.
Suburbs
Residential areas on the outskirts of a city, characterized by lower density and auto-dependent infrastructure.
Squatter Settlement
Informal housing areas built without legal claim; common in rapidly urbanizing developing countries.

Why Do Cities Form?

Cities emerge at locations offering strategic advantages. Geographers identify several key site and situation factors that explain urban origins.

1
Access to resources: Water, fertile land, and raw materials attract initial settlement.
2
Transportation nodes: Rivers, harbors, and crossroads concentrate trade and people.
3
Agricultural surplus: Farming efficiency frees labor for specialization and commerce.
4
Political power: Governments, military defense, and administration anchor urban growth.

The Rank-Size Rule and Primate Cities

The rank-size rule states that the \( n \)-th largest city in a country will be approximately \( \frac{1}{n} \) the population of the largest city:

When a country's largest city is disproportionately larger than this rule predicts, it is called a primate city. A primate city dominates economically, politically, and culturally: think London in the UK or Paris in France.

Visualizing Rank-Size vs. Primate City

Population City Rank 1 2 3 4 5 10M 5M 0 Rank-Size Primate City

Classic Urban Models

Geographers have developed three foundational models to explain the internal structure of cities in North America and beyond:

Concentric Zone
Burgess (1925): City grows in rings outward from a central business district (CBD).
Sector Model
Hoyt (1939): Growth follows wedge-shaped sectors along transport routes from the CBD.
Multiple Nuclei
Harris & Ullman (1945): City develops around several distinct centers of activity, not just one CBD.

Burgess Concentric Zone Model

CBD Zone of Transition Working-Class Middle-Class Commuters 1 2 3 4 5

Comparing the Three Models

Concentric Zone Sector Multiple Nuclei
Shape Rings Wedges Clusters
Growth Driver Distance from CBD Transport routes Multiple activity centers
CBD Role Dominant core Core + corridors One of many nodes
Best Fits Older, compact cities Industrial cities Modern, sprawling cities
Key Criticism Too simplistic Ignores multiple centers Hard to generalize

Global vs. North American Cities

Cities in different world regions follow different structural patterns. The AP exam expects you to recognize how Latin American, African, Southeast Asian, and Islamic cities differ from the North American models.

Latin American
Griffin-Ford model: CBD + commercial spine with elite residential sector; informal squatter settlements on periphery.
Sub-Saharan African
Colonial CBD alongside traditional market zones; informal housing dominates edges of the city.
Southeast Asian
McGee model: port zone CBD with no single dominant center; alien commercial zones alongside government districts.
Islamic
Centered on a grand mosque and adjacent bazaar or suq; residential quarters organized by ethnicity or clan.

World Cities and Global Networks

A world city (or global city) is an urban center that serves as a major node in the global economic system. These cities exert influence far beyond their national borders.

New York Alpha++ London Alpha++ Tokyo Alpha+ Shanghai Paris Dubai Singapore

Suburbanization and Edge Cities

After World War II, automobile ownership, highway construction, and government-backed mortgages fueled massive suburbanization in the United States and other developed countries.

1
White flight: Racial and economic anxieties drove middle-class families from inner cities to suburbs.
2
Highway Act (1956): Interstate highways made commuting from suburbs feasible and fast.
3
Edge cities: Suburban business clusters (e.g., Tysons Corner, VA) that rival or replace the traditional CBD.
4
Urban sprawl: Low-density, car-dependent development consuming farmland and increasing carbon emissions.

How to Analyze a City on the AP Exam

1
Identify the region: Is this a North American, Latin American, African, Southeast Asian, or Islamic city?
2
Locate the CBD: Where is the commercial core? Is there one dominant center or multiple nuclei?
3
Identify residential patterns: Where do wealthy vs. poor populations live relative to the center?
4
Assess informal settlements: Are there squatter zones? Where are they located: periphery or inner zone of transition?
5
Apply the correct model: Match the city's layout to Burgess, Hoyt, Harris-Ullman, Griffin-Ford, or McGee.

Example: The Latin American City Model

CBD Commercial Spine Elite Sector Zone of In Situ Accretion Zone of Maturity Squatter Settlements (Periphery)

Example: Gentrification in Action

Gentrification occurs when wealthier residents move into a previously low-income urban neighborhood, renovating housing and attracting new businesses. This reshapes the social geography of the city.

Before
Affordable rents, ethnic enclaves, local shops, older housing stock, lower property values.
After
Rising rents, displacement of original residents, boutique businesses, renovated buildings, property value spikes.

Common Mistakes on the AP Exam

✕ Confusing Models
Mixing up Burgess (rings) with Hoyt (wedges). Remember: Burgess = circles, Hoyt = pie slices along transport.
✕ Reversing Wealth Patterns
In Latin American cities, the wealthy live near the center along the spine. In North America, wealth moves outward to suburbs.
✕ Rank-Size vs. Primate
The rank-size rule is an ideal distribution, not a description of primate cities. A primate city violates the rule.

Question 1 of 5

According to the rank-size rule, if a country's largest city has a population of 12 million, what would be the expected population of the third-largest city?

Question 2 of 5

Which urban model best describes a city where growth occurs along transportation corridors radiating outward from the CBD in wedge-shaped sectors?

Question 3 of 5

In the Griffin-Ford model of a Latin American city, where are squatter settlements most likely located?

Question 4 of 5

A country where one city is vastly larger than all other cities and dominates the national economy, politics, and culture best illustrates which concept?

Question 5 of 5

Which of the following is a primary consequence of gentrification in urban neighborhoods?