Unit 6.2 — Models of Internal City Structure

Once a city exists and is growing, a second question follows immediately: where inside that city does what kind of activity and what kind of housing end up, and why does that arrangement look so similar across so many unrelated cities? Between the 1920s and the 1940s, American urban sociologists and land economists proposed three competing answers, each built from firsthand observation of real early-20th-century American cities. All three remain the core vocabulary for describing internal city structure on this exam, even though — as the unit closer lesson will stress — none of them describes every city equally well.

The concentric zone model (Burgess, 1923)

Sociologist Ernest Burgess, working from the University of Chicago, published the first of the three models in 1923, based directly on his study of Chicago's own land-use pattern. Burgess argued that a city grows outward from its center in a series of roughly circular rings, each ring representing a distinct land-use zone, expanding outward over time as the city's population grows — a process he described using the biological metaphor of invasion and succession, borrowed from plant ecology, where an outer zone's population gradually pushes into and takes over the zone just inside it.

The rings, from the center outward, are: the central business district (CBD) at the core, where land values peak and commercial, retail, and office activity concentrate; a zone of transition immediately surrounding it, characterized by mixed industrial and low-quality residential land use, deteriorating housing, and the cheapest rents in the city — home to the most recently arrived and lowest-income residents; a zone of working-class homes, housing families who have been in the city longer and moved just one ring outward from the transition zone; a zone of better residences, middle-class single-family housing; and finally a commuter zone at the outer edge, where higher-income residents live at low density and travel back into the CBD for work. The organizing logic is that land value and rent are highest at the center and decline steadily outward, while household income runs the opposite direction — rising the further out you go, because only wealthier residents can afford both the housing and the commute that outer-ring living requires.

The sector model (Hoyt, 1939)

Land economist Homer Hoyt published a revision in 1939 after studying rent patterns across many more American cities than Burgess had examined. Hoyt's core objection was empirical: real cities did not actually arrange land use into clean, uniform rings. Instead, once a particular type of land use established itself along a transportation route radiating outward from the center — a rail line, a major road, a river — that same type of use tended to keep extending further out along the same corridor, rather than curving around into a full ring. The result, in Hoyt's model, is a city divided into wedge-shaped sectors radiating outward from the CBD like slices of a pie, with each sector dominated by one land-use type: an industrial sector following a rail corridor, a high-rent residential sector following a scenic route (a lakefront, a park, a hill), and lower-rent residential sector filling in the remaining wedges.

Hoyt's key insight was that transportation corridors, not uniform distance from the center, drive land-use patterns — and that high-rent residential areas in particular tend to persist and expand outward along the same sector over time, rather than relocating, because wealthier residents moving further out tend to stay within the same general direction from the CBD their predecessors already established. This is why, in many real cities, you can point to "the wealthy side of town" as a genuine, historically stable directional sector rather than a ring at a particular distance.

The multiple nuclei model (Harris and Ullman, 1945)

Geographers Chauncy Harris and Edward Ullman published the third major model in 1945, arguing that by the mid-20th century, growing cities — especially larger ones with the automobile now widespread — no longer organized themselves around one single dominant center at all. Instead, a city develops multiple separate centers, or nuclei, each specializing in a different activity and each generating its own surrounding land-use pattern, rather than all activity radiating from one central point.

Harris and Ullman identified several reasons particular activities cluster into their own nuclei rather than locating near the original CBD: some activities require specialized facilities only available in certain locations (a port, a rail yard, a university campus); some activities benefit from clustering near similar businesses (a garment district, a medical district, an auto-dealership row) because they share suppliers, skilled labor, or customer traffic; some activities are incompatible and actively repel each other (heavy industry and high-end housing do not want to be adjacent, so each pushes the other away into its own separate nucleus); and some activities cannot afford the highest rents found near the most desirable nuclei and so form their own lower-rent cluster elsewhere. The result is a city that looks, on a land-use map, less like rings or wedges and more like a patchwork of specialized districts, each with its own gravitational pull on the surrounding area — a pattern that, once the automobile freed development from having to cluster near rail and streetcar lines, became increasingly common as it more closely matched how many real, especially larger and more polycentric, cities actually grew.

What the three models share, and where they start to diverge

All three models share a set of underlying assumptions worth naming explicitly, because the assumptions are exactly where later critiques (covered in the unit closer) find their opening: each model assumes a single, unified land market driven mainly by private competition for the most valuable, most accessible locations; each was built from observation of large, industrial-era American cities in the first half of the 20th century; and each treats distance from a defining feature (the CBD, a transportation corridor, a specialized nucleus) as the primary variable explaining land use and land value. Where they diverge is in the shape that distance-based logic produces — circles, wedges, or scattered clusters — and in what each treats as the deciding force behind that shape: uniform outward growth over time for Burgess, transportation-corridor path-dependence for Hoyt, and functional specialization plus incompatibility for Harris and Ullman.

Why this matters for the exam

Exam questions on this topic typically hand you a described or diagrammed city layout and ask you to identify which of the three models it matches, or hand you one of the three model names and ask you to identify the correct originator, publication decade, or defining shape (rings, wedges, or scattered nuclei). Memorize the pairing of model, originator(s), and decade precisely — Burgess/1920s/rings, Hoyt/1930s/wedges, Harris and Ullman/1940s/nuclei — since mixing up which economist argued for which shape is one of the most common self-inflicted errors on this topic. Also be ready to explain the underlying mechanism in your own words, not just recite the shape: Burgess's zone of transition housing the newest and poorest arrivals, Hoyt's high-rent sector persisting along one directional corridor, and Harris and Ullman's incompatible-activity logic for why certain nuclei separate from each other. The synthesis lesson at the end of this unit builds directly on all three, so treat the mechanisms here, not just the diagrams, as the material to actually retain.