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Human Geography · Foundations

Cities and Urban Structure

10 min read 5 practice questions
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On this page 9 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Worked example
  6. Key takeaway
  7. Quick check
  8. Study tools
  9. Sources & references

In 30 seconds

A city is not one uniform blob but a set of parts. At its core sits the , the commercial hub with the highest land values. Geographers use classic models — Burgess's concentric rings, Hoyt's sectors, Harris and Ullman's multiple nuclei — to generalize how the rest is arranged. Zoom out, and cities form a hierarchy by size and function, from small towns to primate cities and the world cities that help command the global economy.

Why this matters

Where things sit inside a city shapes commutes, rents, school access, and who lives near opportunity. Reading a city as structured space — a core, rings or sectors, competing nodes — lets planners, economists, and voters reason about zoning, transit, and housing instead of guessing. Scale matters too: a country dominated by one concentrates power and investment differently than one with many balanced centers. And as finance and information flow across borders, a handful of world cities steer the global economy, which is why urban structure is now studied at planetary scale, not just block by block.

The college version

The city as structured space: the CBD

Urban geography treats a city not as a single point on a map but as organized interior space where different activities compete for land. The anchor of that competition is the central business district (CBD), commonly called downtown. It is usually one of the oldest parts of the city and the nodal point where transportation routes converge, so it is the most accessible location in the metropolitan area. Because accessibility is scarce and valuable, land in the CBD commands the highest prices, and the uses that can pay the most — offices, banks, retail, and civic institutions — outbid housing and manufacturing for space. That single mechanism, high accessibility producing high land value, is the thread that runs through every model of urban structure below. It also explains why the CBD tends to build upward rather than outward: when horizontal space is expensive, activities stack vertically.

Three classic models of the North American city

Early-twentieth-century geographers built simplified models of how land use spreads out from the core. The , associated with sociologist Ernest Burgess of the Chicago School (1925), pictures the city as a set of rings around the CBD: a transitional zone of industry and cheaper housing, then successively more established residential rings, out to a commuter zone. Homer Hoyt's (1939) revised this by arguing that growth follows wedges rather than perfect rings — high-rent housing, for example, extends outward along a favored corridor such as a rail line or scenic ridge, so like attracts like along that axis. The of Chauncy Harris and Edward Ullman (1945) drops the assumption of a single center entirely: a large city develops around several specialized nodes — a port, a university, an industrial park, a secondary retail center — because some activities cluster together and others repel each other. All three are generalizations, not maps of any real city, and each has clear limits. They were built on mid-century North American cities and describe them better than cities elsewhere; contemporary metropolitan areas add peripheral 'edge cities' and sprawling mixed suburbs that the tidy ring picture never anticipated. Used carefully, the models are still valuable because they name the forces — accessibility, income sorting, and clustering — that shape real cities.

The urban hierarchy

Step back from a single city and settlements fall into an : many small hamlets and towns, fewer medium cities, and a handful of large metropolises. Larger places sit higher in the hierarchy because they offer more specialized goods and services and serve wider surrounding regions — a village has a grocery store, but only a large city supports a specialist hospital, an international airport, or a stock exchange. Geographers describe this dominance as : a city's functional pull on the territory around it, which is related to but not identical to its raw population. This is where transportation and economic development connect to urban structure, though those are their own topics.

Primate cities and the rank-size rule

Two ideas describe how city sizes are distributed within a country. The states that the nth-largest city is roughly 1/n the size of the largest: the second city is about half the size of the first, the third about a third, the fourth about a quarter, and so on. The United States settlement pattern follows this smooth distribution fairly closely. Many countries instead show urban primacy, where the leading city is disproportionately large relative to the rest — Buenos Aires, for instance, is roughly ten times larger than Argentina's second city, Rosario. Such a dominant city is called a primate city, an idea framed by geographer Mark Jefferson in 1939 as the 'law of the primate city.' Primacy often reflects a country's history of centralized political and economic power. Importantly, a city can be functionally dominant without being strictly primate, so geographers treat rank-size and primacy as two ends of a spectrum rather than rigid laws.

World cities and the global economy

At the very top of the global hierarchy sit world cities, also called global cities: metropolises so integrated into the world economy that their influence reaches far beyond their national borders. Sociologist Saskia Sassen gave the concept its modern shape in The Global City (1991), arguing that as production and finance globalized, a small number of cities — she analyzed New York, London, and Tokyo — became command-and-control centers where corporate headquarters, financial markets, and specialized producer services (law, accounting, consulting) concentrate. These cities coordinate the global economy less through manufacturing than through information and money. A world city is defined by this command function, not by being the largest city in its own country, which is why it is a different idea from a primate city even when the two overlap.

Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Cities are built in layers, like the way a school is arranged. The busiest, most important place — the office and main hall — is in the middle, and everything else spreads out from there depending on how close it needs to be. Long ago, geographers drew simple diagrams to guess the pattern: some said cities grow in rings, some said in slices like a pie, and some said cities have several busy spots instead of just one. None of the diagrams is exactly right, but each points to a real reason places end up where they do. Then, if you compare whole countries, some have one giant city that dwarfs all the others, while others have cities in a neat sliding scale from big to small. And a few super-cities, like New York and London, help run money and business for the entire planet.

Picture it like this

Think of a city like a food court at lunch. The most crowded, most expensive counter sits at the center where everyone passes; smaller stalls, storage, and quiet tables spread outward from there.

Where the picture stops working

The food court has a fixed floor plan set by a designer, but a real city has no single planner — it grows from millions of separate decisions over decades, can sprout several busy 'counters' at once, and keeps changing shape as roads and money move.

Worked example

Suppose a country's largest city has 8 million people. The rank-size rule predicts the second city should be about 8 / 2 = 4 million, the third about 8 / 3 ≈ 2.7 million, and the fourth about 8 / 4 = 2 million. If the real second city has 3.8 million and the third has 2.5 million, the country roughly follows the rule. Now compare Argentina: Buenos Aires is about ten times larger than Rosario, its second city. That gap is far bigger than the rank-size rule predicts (which would put the second city near half), so Argentina shows urban primacy and Buenos Aires is a primate city rather than one step down a smooth ladder.

Key takeaway

Cities have an internal structure organized around the accessible, high-value CBD — captured imperfectly by the concentric-zone, sector, and multiple-nuclei models — and they also sit in a hierarchy of settlements, from smooth rank-size ladders to dominant primate cities and the world cities that help command the global economy.

Quick check

3 questions here, of 5 in this lesson’s practice set. Answers stay hidden until you check.

Question 1 of 3foundational

In models of urban structure, what best describes the central business district (CBD)?

Choose an answer, then check it.
Question 2 of 3intermediate

Which model pictures a city's land use as a series of rings expanding outward from the CBD?

Choose an answer, then check it.
Question 3 of 3advanced

A geographer observes that a large metropolis is organized around several separate business and industrial centers rather than one dominant downtown. Which model best fits this observation?

Choose an answer, then check it.
Practice all 5

Keep learning

Ready to build on this? Continue to the next lesson.

Practice this lesson
Study tools & related lessonsYou’ll learn to · Common mistakes · Easily confused · Key vocabulary · Related

You’ll learn to

  • Define the central business district and explain why it anchors a city's land-use pattern.
  • Distinguish the concentric-zone, sector, and multiple-nuclei models and attribute each to its originators.
  • Explain what an urban hierarchy is and how settlements differ by size and function.
  • Apply the rank-size rule and the primate-city idea to compare national urban systems.
  • Analyze why world cities function as command points of the global economy.

Common mistakes

  • Treating the concentric-zone, sector, and multiple-nuclei models as literal maps of real cities.

    They are simplified generalizations built mainly on mid-century North American cities; real cities blend and depart from all three, adding edge cities and sprawl the models never predicted.

  • Assuming a primate city and a world city are the same thing.

    A primate city is defined by dominating its own national urban system; a world city is defined by its command role in the global economy. A city can be one, both, or neither.

  • Reading the rank-size rule as a strict natural law.

    It is an empirical pattern that fits some countries (like the United States) well and others poorly; many countries show primacy instead. Treat it as a benchmark, not a requirement.

  • Confusing the internal structure of a city with the process of urbanization.

    This topic covers how the inside of a city is arranged and how cities rank by size; the rates and causes of city growth are the separate topic of urbanization.

Easily confused

Concentric-zone model vs. Sector model

Both radiate outward from the CBD, but the concentric model uses complete rings of land use while the sector model uses wedges that follow transport routes, so a high-income area extends along one corridor rather than forming a full ring.

Primate city vs. World city

A primate city is measured against the other cities in its own country (disproportionately large); a world city is measured against the global economy (a command center for finance and services). The reference frame differs.

Rank-size distribution vs. Primate distribution

In a rank-size country the top cities step down smoothly (½, ⅓, ¼ of the largest); in a primate country one city towers over all the rest with a large gap to the second.

Key vocabulary

Central business district (CBD)
The commercial and services core of a city, usually its oldest, most accessible district and the point where transport routes converge; it carries the highest land values.
Concentric-zone model
A model of urban structure that pictures land use as rings expanding outward from the CBD, associated with Ernest Burgess (1925).
Sector model
Homer Hoyt's 1939 model in which land uses grow outward in wedges along transport routes or favored corridors rather than in complete rings.
Multiple-nuclei model
Harris and Ullman's 1945 model in which a city develops around several specialized centers instead of one dominant downtown.
Urban hierarchy
The ordering of settlements by size and by the range of goods, services, and functions they provide to surrounding regions.
Centrality
The functional dominance a city exerts over the territory around it, related to but distinct from its raw population.
Primate city
A country's leading city when it is disproportionately larger and more influential than the next-largest cities; the idea is credited to Mark Jefferson (1939).
Rank-size rule
An empirical pattern in which the nth-largest city in a country is roughly 1/n the size of the largest city.
World city (global city)
A metropolis so integrated into the global economy that it acts as a command center for finance and specialized services beyond its national borders; concept developed by Saskia Sassen.

Sources & references

  1. Introduction to Human Geography (Dorrell and Henderson), 12.4: Urban Patterns — LibreTexts / University of North Georgia Press
  2. Introduction to Human Geography, 12.3: Urbanization — Washington State University Pressbooks (David Dorrell)
  3. Urban Area (encyclopedic entry) — National Geographic Society (Education)
  4. The Global City: New York, London, Tokyo — Saskia Sassen / Princeton University Press

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Researched 2026-08-19

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