---
title: "Multiple-Nuclei Model — AP Human Geography Definition"
description: "The Harris and Ullman multiple-nuclei model (1945) explains cities as growing around several specialized centers, not one CBD. A core AP Unit 6 city model."
canonical: "https://fiveable.me/ap-hug/key-terms/harris-and-ullman-multiple-nuclei-model"
type: "key-term"
subject: "AP Human Geography"
unit: "Unit 6"
---

# Multiple-Nuclei Model — AP Human Geography Definition

## Definition

The Harris and Ullman multiple-nuclei model (1945) is an urban structure model stating that cities develop around several separate centers of activity (nuclei), like an airport, university, or industrial park, rather than radiating from a single central business district.

## What It Is

The multiple-nuclei model, created by geographers Chauncy Harris and Edward Ullman in 1945, says a city isn't built around one downtown. Instead, it grows around several **nuclei**, separate centers that each attract their own kind of activity. A university pulls in bookstores and student housing. An airport attracts hotels and warehouses. A factory district pushes housing away but pulls in workers. Each nucleus becomes its own little gravity center, and the city ends up as a patchwork of specialized districts instead of neat rings or wedges.

The logic behind the model is simple. Some activities benefit from being near each other (offices cluster near offices), while others actively repel each other (nobody builds luxury homes next to a heavy industry zone). Cars and trucks made this possible, since businesses no longer had to crowd around one CBD to be accessible. In the AP CED, this model sits in **EK PSO-6.D.1** alongside the [Burgess concentric-zone model](/ap-hug/unit-6/internal-structure-cities/study-guide/bmmlitd92K8BXI98qRxQ "fv-autolink"), the Hoyt sector model, the [galactic city model](/ap-hug/key-terms/galactic-city-model "fv-autolink"), and bid-rent theory as one of the core tools for explaining the internal structure of cities.

## Why It Matters

This term lives in **Topic 6.5 (The Internal Structure of Cities)** in **[Unit 6](/ap-hug/unit-6 "fv-autolink"): Cities and Urban Land-Use Patterns and Processes**, supporting learning objective **6.5.A**, which asks you to explain the internal structure of cities using various models and theories. The multiple-nuclei model is the bridge between the older single-center models (Burgess, Hoyt) and the newer car-based models (galactic city, [edge cities](/ap-hug/key-terms/edge-cities "fv-autolink")). If you can explain why a city would sprout multiple centers, you understand the shift that automobiles caused in urban form. That makes this model show up constantly in comparison questions where you have to match a described city pattern to the right model.

## Connections

### [Burgess Concentric Zone Model (Unit 6)](/ap-hug/key-terms/burgess-concentric-zone-model)

Burgess assumed everything grows outward from one CBD in rings. Harris and Ullman looked at real mid-century American cities and said that assumption no longer held. The multiple-nuclei model is basically Burgess with the single center broken into pieces.

### [Galactic City Model (Unit 6)](/ap-hug/key-terms/galactic-city-model)

The galactic (peripheral) city model is the next step in the same story. Multiple-nuclei describes several centers inside the city; the galactic model pushes those centers out to the suburban beltway, with edge cities orbiting the old downtown like planets.

### [Edge Cities (Unit 6)](/ap-hug/key-terms/edge-cities)

Edge cities, those suburban clusters of offices and malls near highway exits, are real-world proof of multiple-nuclei logic. Activity centers form wherever accessibility and [clustering](/ap-hug/unit-1/intro-maps-types-maps/study-guide/5yjxIwMtQuImgNT0QdaT "fv-autolink") benefits exist, not just downtown.

### [Central Business District (CBD) (Unit 6)](/ap-hug/key-terms/central-business-district-cbd)

In Burgess and Hoyt, the CBD is the city's one dominant heart. In multiple-nuclei, the CBD still exists but it's just one nucleus among several. Knowing how each model treats the CBD is the fastest way to tell them apart.

## On the AP Exam

Multiple choice is the main home for this term. A typical stem describes a city with separate specialized districts, like one for finance, one for entertainment, one for manufacturing, and one for education, then asks which model fits. The answer is multiple-nuclei whenever you see several distinct activity centers instead of rings or wedges. You should also be ready to identify a multiple-nuclei pattern from a map or diagram. No released FRQ has required this term verbatim, but Unit 6 free-response questions regularly ask you to apply urban models to land-use scenarios, so be ready to explain why activities cluster around separate nuclei (clustering benefits and incompatible land uses) rather than just naming the model.

## Harris and Ullman multiple-nuclei model vs Galactic City Model

Both models have multiple centers, so they get mixed up constantly. The difference is location and era. The multiple-nuclei model (1945) describes several activity centers within the city itself. The galactic city model describes a newer, car-dependent pattern where edge cities and nodes sit on the suburban periphery, connected by ring roads, with the original CBD as just one node in the network. If the question emphasizes suburban beltways and edge cities, think galactic. If it emphasizes specialized districts inside a city, think multiple-nuclei.

## Key Takeaways

- Harris and Ullman proposed the multiple-nuclei model in 1945, arguing that cities grow around several separate centers of activity instead of a single CBD.
- Each nucleus specializes because similar activities cluster together for mutual benefit, while incompatible land uses (like heavy industry and high-end housing) repel each other.
- The model reflects the rise of the automobile, which freed businesses from needing to locate near one central downtown.
- On the exam, pick multiple-nuclei whenever a city is described as having distinct specialized districts, such as a finance center, an entertainment district, and a university area, each acting as its own hub.
- It is listed in EK PSO-6.D.1 alongside the Burgess, Hoyt, galactic, and bid-rent models, so you need to be able to distinguish all of them under LO 6.5.A.
- Multiple-nuclei is the conceptual ancestor of the galactic city model and edge cities, which move those nuclei out to the suburban fringe.

## FAQs

### What is the Harris and Ullman multiple-nuclei model in AP Human Geography?

It's a 1945 urban structure model saying cities develop around multiple separate centers of activity (nuclei), such as airports, universities, and [industrial parks](/ap-hug/key-terms/industrial-parks "fv-autolink"), instead of growing outward from one central business district. It's one of the city models you need for Topic 6.5.

### Does the multiple-nuclei model have a CBD?

Yes, but it's not the only center. The original CBD remains one nucleus among several, which is the big break from the Burgess and Hoyt models where the CBD dominates everything.

### How is the multiple-nuclei model different from the galactic city model?

Multiple-nuclei describes several specialized centers inside a city, while the galactic city model describes edge cities and nodes scattered around the suburban [periphery](/ap-hug/key-terms/periphery "fv-autolink"), linked by highways and ring roads. Galactic is essentially the multiple-nuclei idea pushed outward into the suburbs.

### Why did Harris and Ullman think cities form multiple nuclei?

Two forces drive it. Similar activities cluster together because they benefit from proximity, and incompatible activities repel each other (heavy industry pushes housing away). Cars and trucks made it possible for these clusters to form away from the old downtown.

### What's an example of the multiple-nuclei model on the AP exam?

A classic exam scenario describes a city with separate districts for finance, entertainment, manufacturing, and education, each functioning as its own center of activity. That [pattern](/ap-hug/unit-1/spatial-concepts/study-guide/OwAXsmuGQP2yjp71tEM5 "fv-autolink") of independent specialized hubs is the signature of the multiple-nuclei model.

## Related Study Guides

- [6.5 The Internal Structure of Cities](/ap-hug/unit-6/internal-structure-cities/study-guide/bmmlitd92K8BXI98qRxQ)

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