AP® Human Geography review sheet from Aim for Five (aimforfive.com/geo/units/6/6-2)
Unit 6 · Topic 6.2
6.2 Cities Across the World
Most of today's fastest urban growth is in Asia and Africa, home to many of the world's megacities and metacities. In the United States and other high-income countries, cities have mostly grown outward through suburbanization and sprawl, creating edge cities, exurbs and boomburbs.
Key terms
- megacity
- metacity
- suburbanization
- edge city
- exurb
- boomburb
Megacities and metacities
A megacity is an urban area with 10 million or more people. A metacity, a term from UN-Habitat, has 20 million or more. The UN's World Urbanization Prospects 2025 counted 33 megacities in 2025, up from 8 in 1975, and 19 of them are in Asia.
That report used a new, consistent way of drawing city limits. By that method, Jakarta, Indonesia, was the world's largest city in 2025 with nearly 42 million people, followed by Dhaka, Bangladesh, with about 37 million, and Tokyo, Japan, with about 33 million. Older sources that use each country's own boundaries still list Tokyo first, which is why you'll see different rankings. The UN projects that Dhaka will become the largest by 2050, while Tokyo's population shrinks.
Where cities grow fastest
Megacities exist in core countries (Tokyo, Seoul), but most are now in periphery and semi-periphery countries (Dhaka, Delhi, Cairo, Manila, Mumbai), and that share keeps rising. The fastest growth today is in lower- and middle-income countries in Asia and Africa. These cities grow from both rural-to-urban migration and high natural increase, since many of their residents are young.
Rapid growth often outpaces housing, water, sewer and transit, so many newcomers live in informal settlements (6.10). Cities in core countries, by contrast, tend to grow slowly or even shrink, and they spread outward more than they add people.
Suburbanization and sprawl in the United States
Suburbanization is the movement of people and businesses from central cities to the surrounding suburbs. In the United States it took off after World War II, driven by cars, the Interstate Highway Act of 1956, federally backed mortgages for new single-family homes, and cheap land at the edge of cities. Discrimination shaped it too: many suburbs used covenants and lending practices to keep Black families out (6.10).
Sprawl is the spread of low-density, car-dependent development over large areas at the edge of a city. It uses a lot of land and makes people depend on driving.
As jobs and shopping followed people outward, cities decentralized, meaning activities that once clustered downtown spread across the whole metro area.
- Edge city: a large node of offices and retail at the edge of a metro, usually near a highway interchange. Journalist Joel Garreau popularized the term in 1991; Tysons, Virginia, outside Washington, D.C., is a classic example.
- Exurb: a community beyond the suburbs, still linked to the city by commuting but more rural in feel.
- Boomburb: a fast-growing suburban city of 100,000 or more people that isn't the main city of its metro, like Mesa, Arizona, or Henderson, Nevada.
Worked examples
Try each one yourself first, then open the solution.
- Example 1
Comparing urban growth across regions
Explain one difference between how cities are growing in the United States and how they are growing in sub-Saharan Africa.
Show the solutionHide the solution
- Step 1: Describe the U.S. pattern: slow population growth, outward spread through suburbanization and sprawl.
- Step 2: Describe the African pattern: fast growth from rural-to-urban migration and natural increase.
- Step 3: Connect each to a consequence or cause.
Answer: Model answer: Many U.S. cities are growing slowly in population but spreading outward, as cars, highways and cheap land encourage suburbs and edge cities like Tysons, Virginia. Cities in sub-Saharan Africa, such as Lagos and Kinshasa, are growing rapidly in population because of rural-to-urban migration and high natural increase, which often outpaces housing and services and leads to informal settlements.
Common mistakes
- Assuming all the world's largest cities are in wealthy countries. Most megacities are now in Asia, Africa and Latin America.
- Mixing up edge cities and exurbs. Edge cities are job and shopping hubs; exurbs are mostly residential communities beyond the suburbs.
- Quoting a single 'largest city' without a source. Rankings depend on how city boundaries are drawn.
On the exam
- Expect stimulus questions with a map or table of megacities. Describe where they are and explain why growth is fastest in the periphery and semi-periphery.
- Be ready to define suburbanization, sprawl, edge city, exurb and boomburb, with causes.
Connected topics
Videos
Check yourself
5 questions on 6.2 Cities Across the World. Pick an answer to see if you got it, and why.
Which statement best describes global patterns of urban growth in the early twenty-first century?
Tysons, Virginia, near Washington, D.C., grew from a crossroads into a major cluster of office towers, malls and hotels near the junction of highways. It is best described as
Which factor contributed most to rapid suburbanization in the United States after World War II?
City A: a suburban city that grew from about 60,000 people in 1970 to more than 500,000 today. It is not the main city of its metro area and consists mostly of single-family homes, shopping centers and wide roads.
Place B: a small town about 60 miles from a large city. Over the past twenty years, new houses on large lots have been built on former farmland, and many residents commute long distances to jobs in the metro area.
Place C: a cluster of office towers, hotels and a large mall that grew around a highway interchange in the suburbs, with more office space than many downtowns but few residents.
Descriptions of three places in a hypothetical U.S. metro region
Which terms best describe City A, Place B and Place C, in that order?
All three places are best explained by which broader process?
0 of 5 answered