3Why did Harris & Ullman put forward the model? Pattern of urban land use does not develop around a single center but around a no. of discrete nuclei.Some cities have taken up surrounding settlements or have developed strong suburban areas around the periphery of the city.As the city grows larger, the traditional CBD is no longer sufficient to serve the commercial needs.As a result, additional nodes emerge in outlying districts such as new suburban shopping center, industrial suburb.
4Main features of the model Polycentric / multiple-centredThe model abandoned the CBD as the sole focal point, i.e. suggest alternatively that the zones will develop around a number of quite separate discrete nuclei in addition to the CBD. The number of nuclei depend on the size of the city, i.e. the larger the city, the more numerous and specialized the nuclei are.The city will develop in a cellular structure in which distinctive forms of land use have developed around certain nuclei within the urban area.
5Why multi-nuclei?Different activities have different specific location requirements. Certain specialised functions can only operate where particular facilities are available.e.g. a CBD locates at the point of maximum accessibility.e.g. large industries need cheap land.e.g. high-class housing is drawn to higher parts of a city commanding fresh air and fine views
6Why multi-nuclei?Differences in rent-paying abilities —some activities cannot afford the high rents than others.Manufacturing industry cannot afford the high rents in the inner city and has to locate on cheaper sites.
7Why multi-nuclei?Some land uses repel each other e.g. heavy industry is not found close to high class housing.
8Why multi-nuclei?Tendency for some kinds of eco. activities to cluster together — some activities locate near other for mutual advantages e.g. shops, enabling customers to compare goods and prices
9Why multi-nuclei?Other nuclei develop to aid accessibility around the urban area e.g. develop suburban shopping center to enable people in the suburbs have better access to facilities of the CBD
10Significance of the model the most flexiblefar more widely applicable to modern large cities
11Significance of the model The model matches the dispersal of urban functions with urban sprawl – the dispersal of business activities, retailing activities, residence and manufacturing activities within a large city.made possible by the mass car ownership and other modern transport facilities.With increasing urban sprawl, diseconomies set in.To offset this, the city is disintegreted into a number of nodal regions, each centring on a nucleus which provides many of the functions of the CBDe.g. Los Angeles with its enormous areal spread and rapid rate of pop. growth, the city is arranged in a multiple-nucleated form.
12Significance of the model this model tells more about the concept of agglomeration, forces of attraction and repulsion. These explain the complexity of present day urban functions.
13Significance of the model This model does not apply appropriately to each and every city, but rather suggests a no. of general principles which are relevant to the land use pattern of most cities.It may be taken as a guide to think about the structure of cities rather than a rigid generalization about urban forms