The multiple nuclei model is an ecological model put forth by Chauncy Harris and Edward Ullman in the 1945 article "The Nature of Cities." The model describes the layout of a city. It notes that while a city may have started with a central business district, similar industries with common land-use and financial requirements are established near each other. These groupings influence their immediate neighborhood. Hotels and restaurants spring up around airports, for example. The number and kinds of nuclei mark a city's growth.
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 park). The model is suitable for the big and expanding cities.The number of nuclei around which the city expands,depends upon the situational as well as historical factors. Multiple nuclei develop because: 1). certain activities require specialized facilities eg. ports, railway stations etc. 2). Certain activities tend to stay apart e.g. heavy industry, airport etc. 3). Certain activities are found together to their mutual advantage e.g. University, bookstore,coffee shops, Dhabas, etc.
Sector model is formed by Great Park from Korea. This model shows how many people live in a specific area.