Master urban models, the rank-size rule, primate cities, gentrification, suburbanization, global cities, smart growth, and every urban geography concept on the exam.
Unit 6 covers the geography of cities — how they are structured, why they grow where they do, and how urban policies shape who benefits and who is displaced. It accounts for roughly 12–17% of the AP exam.
The unit's core is the three classic urban land use models: the Burgess Concentric Zone Model (rings from the CBD), the Hoyt Sector Model (wedge-shaped sectors along transportation corridors), and the Multiple Nuclei Model (multiple activity nodes rather than one CBD). You'll learn when each model applies — and crucially, when it doesn't.
Urban hierarchy concepts — rank-size rule, primate cities, central place theory, and global cities — explain why cities exist in different sizes and serve different functions. Contemporary processes like gentrification, suburbanization, urban sprawl, edge cities, and smart growth explain how cities are changing today. The unit concludes with the consequences of housing policy — redlining, blockbusting, exclusionary zoning — and their lasting geographic imprints on urban inequality.
Key terms preview
A taste of what you’ll find in The Essentials and Flashcards.
Primate City
A city at least twice the size of the next largest, dominating the nation's economy and culture.
Burgess Concentric Zone Model
Rings of land use from the CBD outward — transition zone, working-class, middle-class, commuter.
Gentrification
Higher-income residents move in, raise property values, and often displace existing residents.
Urban Sprawl
Uncontrolled low-density outward expansion dependent on automobiles.
Smart Growth
Compact, walkable, mixed-use, transit-oriented development as an alternative to sprawl.
Bid-Rent Theory
Land values decrease with distance from the CBD; different users outbid each other at different distances.
1. Cities are organized according to models — but models have limits
The Burgess, Hoyt, and Multiple Nuclei models describe different patterns of urban land use. Each reflects a specific historical context (industrial city, automobile era, modern polycentric city). Knowing when each model applies — and when it doesn't — is more important than memorizing zones.
2. Urban hierarchies explain the size and function of cities
The rank-size rule predicts a smooth hierarchy of city sizes in a developed country. When a primate city dominates instead, it signals uneven development and economic concentration. Central place theory explains why cities of different sizes provide different services at different scales.
3. Urbanization in the developing world looks different from historical models
Most of today's urban growth is in developing countries — producing megacities, informal settlements, and rapid expansion without the infrastructure to support it. Models developed from North American/European cities (Burgess, Hoyt) don't describe cities like Lagos, Mumbai, or São Paulo as well as they describe Chicago.
4. Urban policy shapes who benefits from cities and who is displaced
Gentrification, redlining, blockbusting, urban renewal, and smart growth all represent policy choices (or policy failures) that profoundly affect who can live where. Understanding the geographic consequences of housing policy is central to AP Human Geography Unit 6.