Multiple Nuclei Theory

 Multiple nuclei model of 1945 by C.D. Harris and Edward L. Ullman is based on the argument that the cities have multiple growth points or “nuclei” around which growth take place. This model was given in an article by them “The Nature of Cities”. This model is based on the structure of Chicago just like the Burgess model or Concentric zone model of 1925. It can be considered as an attempt to explain the structure of the city taking into account the complexity and growth over time. Harris and Ullman argued that a city might start with a single central business district (CBD), but over the time the activities scatter and gets modified. The scattered activities attract people from surrounding areas and act as smaller nuclei in itself. These small nuclei gain importance and grow in size and start influencing the growth of activities around them. The basic assumption of this theory is that "cities are not homocentric" but they rather have many mini centres which play a significant role in the development of a city. These mini centres originally developed independently with the specialized advantages that they offered or similar activities clustering in these areas. 

The need for this model was to provide a more realistic explanation of the cities. The influence of cars on personal travel and greater movement of goods offered opportunity in different places instead of concentrating all economic activities in one place. People started optimizing their business for maximum profit by locating at a different place and bringing down their rent with a slight increase in transportation cost. Whereas some activities like industrial areas create pollution and are thus preferred to be located away from residential areas. This model is considered to be more suitable for cities which are large and expanding.

Assumptions for Multiple Nuclei Model 

• The land is not flat – This provides a more practical application of the multiple nuclei model and is an improvement over the Burgess model. It is difficult to find flat land for big cities, and the terrain features affects the activities, development and direction of growth of an urban area. 
• Even distribution of resources – Resources are evenly distributed within the city, no one enjoys privileges or have exclusive access to resources. 
• Even distribution of people in residential areas – People are distributed homogeneously and not concentrated in a particular area or pocket. This is essential as an unevenly distributed population has a direct impact on markets. 
• Even transportation cost – Transportation cost is even in the city and not influenced by location. 
• Profit maximization – A particular activity will locate itself where maximum profit can be earned. For this, a different combination of rent, transportation costs, labor cost, proximity to market may be tried, and the combination which yields the best result gives the final location for the activity. This location also takes into account the restrictions over the activity and the need to be separated from other non compatible activities such as locating residential areas away from industrial, locating large industries with more accessibility to reduce transportation cost and to ease the movement of goods.

                                                                 Multiple nuclei model 

Multiple nuclei theory is further divided into nine major areas. 

1) Central Business District 

2) Wholesale or light manufacturing 

3) Low income residential 

4) Medium income residential 

5) High income residential 

6) Heavy industry 

7) Outlying business district 

8) Residential suburb (Suburb - an outlying part of a city or town) 

9) Industrial suburb 

Limitations and criticism of the Multiple Nuclei Model

Multiple nuclei model was considered much better than the previous simple models which attempted to explain the structure of urban areas. However, this model also had its limitations and could not be applied to many cities and did not entirely explain the structure of urban areas. Formation of well-defined zones or “nuclei” required the considerable size of the city as the small or new towns do not have a very well defined location because of which they are usually scattered. Another drawback is the limited activities which are considered in the model along with the very rigid and specific boundaries of the activities. Some other disadvantages include: 

• Negligence of the height of buildings. 
• Non-existence of abrupt divisions between zones. 
• Each zone displays a significant degree of internal heterogeneity and not homogeneity. 
• Unawareness of inertia forces. 
• No consideration of the influence of physical relief and government policy. 
• The concepts may not apply to Asian cities with different cultural, economic and political backgrounds.