Ecological Models of Urban Form

Ecological models of urban form describe and explain the spatial patterns taken by the distribution of people, buildings, and activities across a city’s terrain. This orderly set of spatial arrangements is known as the city’s land use pattern or spatial form. Through the years eco logical researchers have identified three major models of the geometry of city form: concentric zone, sector, and multiple nuclei. While the three models are conceptually distinct, in the actual development of most cities various elements from the three models become uniquely combined into a spatial pattern that gives each city its own individual spatial geometry. Each of the three models was developed to explain urban morphology in industrial cities of the twentieth century. The concentric zone model was presented by Ernest Burgess in 1925. The sector (Hoyt 1939) and multiple nuclei (Harris & Ullman 1945) models were presented later as alternatives to the concentric zone model. Through time the three have become intellectually linked and widely considered as ‘‘the classic models of urban land use.’’ They are ‘‘classic’’ in the sense that the three models have stood the test of time and have proven to be catalysts of research on cities in both developed and developing societies.


The three models share common assumptions: (1) that the city is growing in population and expanding in economic activities; (2) a relatively free land market that is responsive to the economic principles of supply and demand with little in the way of government regulation; (3) an economic base that is mainly a mix of industrial commercial activities; (4) private ownership of property; (5) specialization in land use; (6) a transportation system that is fairly rapid and efficient, and generally available in terms of cost to the majority of the population; and (7) freedom of residential choice, at least for the higher socioeconomic strata. Even though sharing these assumptions, the three models predict different spatial geo metries (see Figure 1).

 Classic models of urban spatial geometry

Figure 1 Classic models of urban spatial geometry.

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Concentric Zone Model

For the Chicago School sociologists (1914–45), Chicago was the prototypical growing industrial city. What was true for Chicago, they argued, was true for most others. Chicago was both their window on city life and their laboratory for community study. The concentric zone model described Chicago, they argued, and, in essence, described other cities as well.

The concentric zone model, attributed to Ernest Burgess, posits a city undergoing rapid population and economic growth. As different population groups, industrial enterprises, and organizations come to the city, an enormous land market competition develops for highly prized locations. The groups with the most available resources (e.g., business and industry, the upper class) are able to obtain the locations they desire while those with fewer resources (e. g., impoverished immigrant groups) have to make do elsewhere. In 1929 Robert Park called the city, through the operation of its land market, a ‘‘great sifting and sorting mechanism . . . so that every individual finds, eventually, either the place where he can, or the place where he must live’’ (Park 1952: 79).

Central location is valued most highly since the old industrial city had but one vital down town center. Central location minimizes transportation costs to all other locations in the city. Consequently, land values at the city’s center soar and can only be afforded by the most resource laden groups – typically, business and industry. The central business district (CBD) forms the organizing node of the city and is identified as Zone 1 of the model. It includes banks and other financial institutions, corporate offices and headquarters, large department stores and specialized retailers, museums, hotels and night clubs, bars and restaurants, theaters and other entertainment venues, and government administrative offices.

Zone 2, the zone in transition, is located around the CBD on all sides. It is in the process of shifting from residential to industrial commercial land uses as the growing CBD spills its various activities into it. It is an area of intense land speculation and profit taking by property owners. The area’s increasing blight and deterioration drive out the middle and working class residents. Their leaving makes the zone an available place of residence for those groups that cannot obtain housing elsewhere – the segregated racial and ethnic minorities, the socially stigmatized, the downwardly mobile, and those seeking impersonality, anonymity, and seclusion. Slums, prostitution, crime, mental and physical illness, and the drug war flourish in the zone in transition. It is a socially distressed area inhabited by socially distressed individuals.

Just beyond the zone in transition is found Zone 3, the zone of workingmen’s homes. It is a blue collar neighborhood inhabited by stable families where ‘‘respectability’’ is a driving ethos. The housing is neat and tidy and the residents are alert and ‘‘on guard’’ against incursions of minorities from the zone in transition. Residential invasions of the poor and ethnic minorities are usually met with resistance. Blockbusting realtors operate in the zone to open housing opportunities for those minority group members moving up socioeconomically and out spatially. Once a ‘‘tipping point’’ has been reached and inmigrating minorities flood the zone, the working class residents flee further out, typically into the adjacent Zone 4, the zone of better residences, which houses the middle class. In turn, the middle class moves further out in response to the perceived down grading of its neighborhoods by the newcomers. It relocates to the next adjacent zone, the commuters’ zone, which at one time housed the city’s upper crust. Later Burgess identified two additional zones in the metropolis – the agricultural districts and the metropolitan hinterland (Burgess 1930).

The shifting of people and activities from one zone to another according to this model resembles the pattern that is observed when a pebble is tossed into a lake. The concentric ripples it creates follow and run into each other in their outward rush. The turnover rate of urban neighborhoods from one population type or activity type to another is governed by several factors. First is the rate of growth in people and activities that demand housing or buildings. Second is the rate of construction of dwellings, industrial buildings, and commercial confines. Third is the investment decisions made by developers, financial institutions, and political regimes. If construction lags behind population and economic growth, stagnation and the piling up of people and activities take place. Demand for developed land increases and the prices for developed parcels escalate. If construction exceeds population and economic growth, vacancy rates rise and land prices decline, but new opportunities are created that may serve to attract future growth. Or, in the extreme, with high vacancies and little growth, a collapse of the local development economy may take place which sends the city into economic depression.

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Sector Model

On the basis of studying 142 American cities, Homer Hoyt (1939) argued that, contrary to the concentric zone model, the city’s urban geometry is better described by a sector pattern of land development. The distributions of rents and the city’s socioeconomic status groups are organized in homogeneous, pie shaped wedges or sectors that run from the city’s CBD to the periphery. The characteristic land use, activity mix, and population composition for any sector are different from those sectors adjacent to it. The implication is that if one were to drive from the CBD to the periphery while remaining in the same sector, one would remain in generally the same type of land use, resident population composition, and activity mix. The concentric zone model provides the driver with a much different view of the city. As one travels from the CBD to the periphery, regardless of direction, one passes through the same gradation of an ever increasing status composition of neighborhoods.

The sector model is based on an axial conception of the city. It incorporates Richard Hurd’s (1924 [1903]) idea that growth and development first take place along main transportation routes from the city’s center to the hinterland; these include rail lines, highways, and navigable bodies of water. At some point, it becomes cheaper in travel time and money to develop the open land between the axes than to continue the outward push along the axes. As the area between the axes becomes filled, another cycle begins with development shifting to the axes again and pushing out along them into the undeveloped hinterland.

In a city with a sector spatial geometry, sectors of industry, warehousing, and poor quality land tend to be surrounded by sectors of low income and working class residents. Middle class housing sectors tend to buffer those of upper status from the sectors of low income, industry, and noxious activities. The high status populations command the most desirable sites in the city. The high rent sectors tend to occupy high ground that is free from risk of floods and deluxe apartment areas tend to be established near the business centers in old established residential areas. Low rent areas and the areas occupied by the poor and marginalized race and ethnic groups tend to be located on the opposite side of the city from the high income sector.

The location and movement of the sectors occupied by the wealthy and upper socioeconomic groups have a major impact on the location of the other sectors. Hoyt’s model argues that high rent residential growth tends to proceed from its given point of origin along established lines of travel or toward another existing nucleus or trade area. The high rent sectors tend to spread along lake, bay, river, and ocean ports where the waterfronts are non industrial. High rent residential districts tend to grow toward open country, away from ‘‘dead end’’ sectors that prevent expansion by natural or artificial barriers, and toward the homes of the community leaders. The growth of high rent neighborhoods continues in the same direction for a long time. Real estate developers may bend the direction of high grade residential growth, but they cannot negate or reverse the effects of the general principles embodied in the model.

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Multiple Nuclei Model

Unlike the other models, the multiple nuclei model of Chauncy Harris and Edward Ullman (1945) does not view the city as being organized around the CBD. Rather, it postulates that there are a number of different growth nuclei, each of which exerts influences on the distribution of people, activities, and land uses. Each nucleus specializes in markedly different activities, ranging from retailing through manufacturing, education and health services to residential. Nuclei vary in size. Some are large, such as the industrial sites; other are small, such as a strip shopping center. Thus, the city’s spatial geometry is much like a patchwork quilt of differing nuclei that are not organized around a single center. The CBD is but one of several functionally important nuclei.

The multiple nuclei model uses four basic principles to explain both the emergence of separate nuclei and the change in them through time. (1) Certain activities require specialized facilities located in only one or a few sections of the metropolis, as seen in the case of manufacturing plants requiring large blocks of undeveloped land located near rail lines. (2) Certain like activities profit from adjacent congregation, as seen in the clustering of retail establishments into malls and shopping centers. (3) Certain unlike activities are antagonistic or detrimental to each other, as seen in the case of manufacturing plants and upper class residential developments. (4) Certain activities are unable to afford the costs of the most desirable locations, as seen in the case of low income residential areas and high land with a much sought after view.

The number and mix of nuclei in a city vary greatly. Larger cities have more nuclei than do smaller places, and they tend to be more specialized in the larger community. For example, a small city may have a retailing nucleus, but in a larger city the separate retail activities may spin out into their own nucleus, as seen in the ‘‘diamond’’ district in New York City. Some nuclei have existed from the origins of the city, as seen in the CBD; others developed as the city grew, such as ethnic enclaves established by arriving immigrant groups, and through urban redevelopment as one land use supplants another, as in the case of an arena project being built on the site of a former prison.

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Models in Combination

In examining the comparative utility of the three models, researchers have found that in many cities socioeconomic status tends to vary by both sector and distance. That is, some sectors tend to contain a larger percentage of the affluent than do others, and there is a general tendency for the socioeconomic standing of neighborhoods to increase with distance from the CBD. Studies have also shown that housing types and values often vary by sector. Regard less of the extent to which a city’s spatial geometry approximates concentric zones or sectors, overlaying the whole pattern tends to be numerous nuclei devoted to such things as educational campuses, medical complexes, race and ethnic group ghettoes and enclaves, industrial plants, parks, and historic districts.

In applying the models to other societies, researchers have identified elements of the three models in the geometry of spatial structure of their cities. A main difference between the geometry of cities in developed and developing societies is that in the developing societies, socioeconomic status tends to be inversely related to distance from the core, while in cities in developed societies, status tends to have a direct relationship with distance. Some have suggested that as cities in developing societies increasingly become part of the global network, they experience economic, social, and political changes and those changes are manifest in the transition of their spatial geometries to a pat tern consistent with the patterns of cities in developed societies (Schwirian 1983).

Increasingly, researchers have argued that the spatial geometry of post industrial cities such as Los Angeles does not conform to the classic models. Their origin lies not in the industrial centralization of the twentieth century as assumed by the classic models, but, rather, in the decentralized and dispersed multicentric metropolitan region of the postmodern age (Dear 2001).

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  1. Burgess, E. W. (1925) The Growth of the City. In: Park, R. E., Burgess, E. W., & McKenzie, R. W., The City. University of Chicago Press, Chicago.
  2. Burgess, E. W. (1930) The New Community and its Future. Annals of the American Academy of Political and Social Science 149: 161, 162.
  3. Dear, M. J. (Ed.) (2001) From Chicago to LA: Making Sense of Urban Theory. Sage, Thousand Oaks, CA.
  4. Harris, C. D. & Ullman, E. L. (1945). The Nature of Cities. Annals of the American Academy of Political and Social Science 242: 7-17.
  5. Hawley, A. (1950) Human Ecology. Ronald Press, New York.
  6. Hoyt, H. (1939) The Structure and Growth of Residential Neighborhoods in American Cities. Government Printing Office, Washington, DC.
  7. Hurd, R. M. (1924 [1903]) Principles of City Land Values. Record and Guide, New York.
  8. Park, R. E. (1952) Human Communities. Free Press, Glencoe, IL.
  9. Schwirian, K. P. (1983) Urban Spatial Arrangements as Reflections of Social Reality. In: Pipkin, J. S., LaGory, M. L., & Blau, J. R. (Eds.), Remaking the City: Social Science Perspectives on Urban Design. State University of New York Press, Albany.

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