AP Human Geo models: Multiple nuclei, sector, concentric zones

Unit 6 of AP (Advanced Placement) Human Geography (cities and urban land use) leans heavily on three classic urban models: the concentric zone model (Burgess, 1925), the sector model (Hoyt, 1939), and the multiple nuclei model (Harris and Ullman, 1945). All three try to describe how activities and land uses arrange themselves inside a city. They contradict each other on purpose: each was designed to fix a shortcoming the previous one exposed.

This guide walks through each model with what it looks like, what it assumes, which real city it was built to describe, and how FRQ rubrics tend to reward comparisons. If you'd rather practice the wider Unit 6 content, Cognito's AP Human Geography notes cover urban structure and every other CED subtopic.

Ernest Burgess built the concentric zone model on 1920s Chicago. Picture a bullseye. The center is Zone 1: the central business district (CBD), where retail and offices concentrate because land is most accessible. Ringing that is Zone 2: a transitional zone of aging housing being encroached on by industry, home to the poorest recent arrivals. Zone 3 is working-class residential; Zone 4 is middle-class residential; Zone 5 is a commuter zone of suburbs and detached homes reached by streetcar or rail.

The underlying idea: land values are highest at the CBD and decline outward. As the city grows, each ring pushes outward and takes over what was previously the ring beyond it, which is why the transitional zone is defined by its instability.

Assumptions Burgess made and where they break: flat terrain (no rivers, hills or coasts breaking the rings), a single central point of economic activity, and no transport routes distorting the pattern. Chicago fit this reasonably well in 1925; most cities don't.

Homer Hoyt looked at the concentric zone model in 1939 and thought: transport lines matter more than rings. His sector model replaces Burgess's bullseye with wedges (pie slices) radiating outward from the CBD, each following a transport corridor.

Inside each sector, land use tends to stay consistent as the city grows. If a sector starts as working-class housing near industry along a rail line, it stays working-class as the city expands along that rail line. High-income residential sectors follow the best amenities (waterfronts, high ground, universities); low-income sectors cluster near heavy industry.

Assumptions: transport corridors dominate residential patterns, and sectors are locked in early. Hoyt drew on data from 142 American cities in the 1930s and found this pattern held better than concentric zones. FRQs like this model for questions about industrial location and residential income sorting.

Chauncy Harris and Edward Ullman published the multiple nuclei model in 1945 as a critique of both earlier models. Their point: cities have grown so large that no single CBD dominates. Instead, activities cluster around several separate nodes (nuclei). One node might be the original CBD, another might be an airport-linked office park, another an outlying industrial district, another a university with associated student housing.

Why several nodes rather than one? Some activities benefit from being together (retail clusters near retail; universities attract related services); some activities repel each other (heavy industry pushes residential away; wealthy neighborhoods sort away from noisy uses). Different rents suit different uses. As cities exceed a certain size, no single center can serve every function efficiently.

Assumptions: a large enough city (small towns still have a single CBD), diverse land uses, no severe physical barriers. This model fits modern American metropolitan areas better than either of its predecessors, which is why it is often used to describe post-WWII US cities.

The three classic models above are all built on North American cities. The CED also expects students to know models developed for other regional contexts: the Latin American (Griffin-Ford), Southeast Asian (McGee) and sub-Saharan African (de Blij) city models, as well as the galactic city (peripheral) model for modern North American metros. Two of these are summarized below.

Griffin-Ford (Latin American city) model: a spine of high-income development extends from a colonial CBD out to a mall or elite district. Surrounding this spine is a zone of maturity (middle-class), then a zone of in situ accretion (mixed), then a zone of peripheral squatter settlements. Disamenity sectors (very poor, often extralegal) cut into the pattern along rivers or in unbuilt areas.

McGee (Southeast Asian city) model: focused on the port. Government zone, commercial zones (Western commercial, alien commercial dominated by Chinese merchants), mixed land use, market gardening. No single dominant CBD; several functional zones organized around the port.

On FRQs, students who can only describe US models struggle when asked about cities in Sao Paulo, Jakarta or Mexico City. Learning at least one non-Western model with a specific example (Griffin-Ford applied to Mexico City, McGee applied to Jakarta) is high-yield revision.

Every AP Human Geography FRQ has seven one-point parts (A through G). An urban-models question might ask you to identify or describe a model in an early part, apply it to a city or stimulus in the middle parts, and explain its limitations or a related concept (bid-rent theory, edge cities, gentrification, or a comparison to another model) in the later parts.

Students often lose points on the limitations part. Rubrics don't just accept 'this model doesn't perfectly describe city X'; they want a specific mechanism (a physical barrier, a colonial history, a specific transport network, or a policy) that explains why. Learn each model with at least one specific city and one specific reason the fit is imperfect.