The multiple nuclei model is an economical model created by Chauncy Harris and Edward Ullman in the 1945 article "The Nature of Cities".

Theory of Urban Growth

The model describes the layout of a city, based on Chicago. It says that even though a city may have begun with a central business district, or CBD, other smaller CBDs develop on the outskirts of the city near the more valuable housing areas to allow shorter commutes from the outskirts of the city. This creates nodes or nuclei in other parts of the city besides the CBD thus the name multiple nuclei model. Their aim was to produce a more realistic, if more complicated, model. Their main goals in this were to:
 Multiple_nuclei_model.svgMove away from the concentric zone model
To better reflect the complex nature of urban areas, especially those of larger size
Harris and Ullman argued that cities do not grow a single nucleus but several separate nuclei. Each nucleus acts like a growth point.
The theory was formed based on the idea that people have greater movement due to increased car ownership. This increase of movement allows for the specialization of regional centers (e.g. heavy industry, business parks, retail areas). The model is suitable for the large, expanding cities. The number of nuclei around which the city expands depends upon situational as well as historical factors. Multiple nuclei develop because:
  • Certain industrial activities require transportation facilities e.g. ports, railway stations, etc. to lower transportation costs.
  • Various combinations of activities tend to be kept apart e.g. residential areas and airports, factories and parks, etc.
  • Other activities are found together to their mutual advantage e.g. universities, bookstores and coffee shops, etc.
  • Some facilities need to be set in specific areas in a city - for example the CBD requires convenient traffic systems, and many factories need an abundant source of water
  • Certain events benefit from the adjacent distance like the positions of factories and residence.
  • In some cases, some constructions are located in less-than-ideal locations, often due to outside factors such as rent.
For more information & further reading check Multiple Nuclei Model under Settlement Geography