ZIMSEC O Level Geography Notes: Settlements: Harris and Ullman’s Multi-nuclei model (1945)
They made their study well after the other two models had been published and thus had the benefit of hindsight and cities had since grown in size.
They realized the fact that modern cities have a more complex structure than described by the Concentric and Sector models
Cities usually grow from several independent nuclei rather than or in addition to the main CBD.
These cores include sub-urban shopping centers in most modern cities.
Each of these nucleus acts as a point of growth and usually has some of the functions found in the main CBD and other nuclei for example it might have banks, shopping malls, supermarkets etc
For example Sam Levy shopping center, Kamphinsa, Westgate, Makoni shopping centers
These centers grow with time to merge with each other to form one large urban center.
Harris and Ullman were able to study later urban settlements that had satellite residential and industrial suburbs in their model.
If the main city becomes too large and congested some functions may disperse to form new nuclei.
Multiple nuclei thus develop out of the need for quick access to the center, to keep certain land uses apart and to decentralise.
The city of Harare closely approximates this model with the main large CBD at the center and various nuclei in the form of shopping centers such as Borrowdale, Same Levy, Machipisa in Highfield, Kamphinsa in Greendale, Westgate, Pendennis in Mt Pleasant etc.
It also has satellite towns in Ruwa and Chitungwiza.