Classic North American models of urban structure

Cities develop distinct internal structures, which refer to the patterns of land use, population distribution, and economic activities within urban areas. These patterns vary due to factors like physical geography, transportation, and economic forces. Several classic models, developed primarily for North American cities in the early to mid-20th century, help explain these structures by simplifying complex urban growth into visual frameworks. Each model builds on the idea of a central business district (CBD) - the commercial and economic core of a city where land values are highest.

Burgess concentric-zone model

The Burgess concentric-zone model, created by sociologist Ernest Burgess in 1925, describes city growth as a series of expanding rings or zones around a central point. It assumes cities expand outward from the center due to population growth and immigration, with each zone having specific land uses.

Key zones in the Burgess model:

• Zone 1: Central business district (CBD) - The innermost ring with high-rise offices, shops, and intense commercial activity.
• Zone 2: Zone of transition - An area of mixed residential and industrial use, often with older housing and factories, prone to urban decay.
• Zone 3: Zone of independent working-class homes - Stable residential areas for blue-collar workers, with modest single-family homes.
• Zone 4: Zone of better residences - Middle-class suburbs with newer, larger homes.
• Zone 5: Commuter zone - Outermost ring of affluent suburbs where residents travel to the city center for work.

This model highlights how social groups sort themselves by income and ethnicity as the city grows.

Hoyt sector model

The Hoyt sector model, developed by economist Homer Hoyt in 1939, modifies the concentric-zone idea by emphasizing sectors or wedges that extend from the city center along transportation routes. It recognizes that urban growth follows lines like railroads or highways, creating pie-shaped districts rather than uniform rings.

Key features of the Hoyt model:

• Central business district (CBD) - Remains the core, with sectors radiating outward.
• Industrial sectors - Develop along transportation corridors, such as rivers or rail lines, due to easy access for goods movement.
• Residential sectors - High-income housing forms in desirable sectors (e.g., away from industry), while low-income areas cluster in less favorable ones.
• Sector persistence - Once established, sectors maintain their character as the city expands, influenced by rent gradients and social preferences.

This model accounts for directional growth rather than symmetrical expansion.

Harris and Ullman multiple-nuclei model

The multiple-nuclei model, proposed by geographers Chauncy Harris and Edward Ullman in 1945, suggests that cities develop around multiple centers or nuclei (distinct hubs of activity) rather than a single CBD. This reflects post-World War II urbanization, where cars and suburbs led to decentralized growth.

Key elements of the multiple-nuclei model:

• Multiple nuclei - Separate centers for activities like retailing, industry, or education, each attracting related land uses.
• Examples of nuclei - A downtown CBD, an airport, a university, or a port, each forming its own cluster.
• Decentralized structure - Nuclei grow independently, leading to a patchwork of districts rather than ordered zones or sectors.
• Influencing factors - Compatibility of land uses (e.g., homes near schools) and transportation advancements that allow spread-out development.

This model explains why modern cities often lack a dominant center.

The galactic city model and bid-rent theory

As cities evolved in the late 20th century, new models emerged to address suburbanization and automobile dependency. These build on earlier ideas but incorporate edge cities (suburban hubs with offices and retail) and economic principles like land value gradients.

Galactic city model

The galactic city model, also known as the peripheral model, describes post-industrial cities where the traditional CBD loses dominance to a ring of suburbs connected by beltways (circular highways). Developed in the 1960s, it portrays the city as a "galaxy" with the old downtown as a fading core and new edge cities as surrounding "planets."

Key components of the galactic city model:

• Central city decline - The original CBD shrinks as businesses move outward.
• Edge cities - Suburban nodes with offices, malls, and entertainment, functioning like mini-cities.
• Beltway connections - Ring roads link these areas, enabling sprawl and reducing reliance on the center.
• Examples - Cities like Detroit or Atlanta, where suburbs have their own economic gravity.

This model reflects the shift to car-based lifestyles and decentralized economies.

Bid-rent theory

Bid-rent theory explains how land use patterns form based on the willingness of different users to pay rent, which decreases with distance from the CBD due to accessibility. It assumes a monocentric city (one with a single center) where competition for prime locations drives up costs.

Core principles of bid-rent theory:

• Rent gradients - Land value peaks at the CBD and falls outward, creating curves for different uses (e.g., retail bids highest for central spots).
• Land use allocation - Commercial activities occupy the center (high rent tolerance), residences farther out (lower tolerance), and agriculture at the edges.
• Influencing factors - Transportation costs and accessibility determine bid levels; better transit flattens the curve.

This theory underpins many urban models by linking economics to spatial patterns.

Urban models from Latin America, Southeast Asia, and Africa

Urban models from regions outside North America adapt classic theories to local contexts, accounting for colonialism, rapid urbanization, and informal economies. These highlight how physical geography, history, and resources shape cities differently across the globe.

Latin American urban model

The Griffin-Ford model for Latin American cities, developed in 1980, features a central elite spine (a corridor of high-end development) surrounded by zones of varying wealth, reflecting colonial legacies and inequality.

Key features:

• Commercial spine - An elite corridor with modern offices, malls, and affluent housing extending from the CBD.
• Zones of maturity and in situ accretion - Middle-class areas with improving infrastructure, transitioning to squatter settlements (informal housing built by residents).
• Periferia - Outer rings of poverty with rapid growth and limited services.
• Influences - Colonial plazas, rapid migration, and economic disparity create this structure.

Southeast Asian urban model

The McGee model for Southeast Asian cities emphasizes desakota regions (hybrid zones blending rural and urban land uses), driven by dense populations and economic booms.

Key features:

• Core urban zone - A dense CBD with ports and commerce.
• Desakota periphery - Extended areas mixing agriculture, industry, and housing, without clear boundaries.
• Influences - Rice farming, foreign investment, and informal sectors shape this fluid structure.

African urban model

Sub-Saharan African models often show colonial imprints, with a central area influenced by European planning surrounded by informal settlements.

Key features:

• Colonial CBD - Formal districts with government and business functions.
• Informal sectors - Rapidly growing townships with markets and self-built housing.
• Ethnic enclaves - Areas divided by tribal or migrant groups.
• Influences - Resource extraction, poverty, and post-colonial migration drive fragmented growth.

Strengths, weaknesses, and limitations of urban models and theories

Urban models and theories simplify complex realities to aid understanding, but they have varying applicability. Evaluating them involves considering their context, such as time period, geography, and cultural factors.

Comparison of model strengths and weaknesses

These evaluations show that no model is universal - they work best when combined or adapted to specific contexts, such as physical resources or cultural histories.