Cities become possible when an agricultural surplus develops together with improved means of transportation and tend to be located at breaks in transportation. The most significant current developments in city structure are the metropolitan area including the suburb which accounts for current population growth.
The city pulls people from various corners towards its nucleus. The rural people faced with various economic problems are attracted by the city and start moving towards the cities. The city provides ample opportunities for personal advancement. It is the centre of brisk economic, commercial, artistic, literary, political, educational, technological, scientific and other activities. Cities are not only the controlling centers of their societies but also the source of innovation and change. They act as the source of new ideas for production, the pace -setters for consumption, guardians of culture and conservers of order in society. Consensus and continuity in a society are maintained from the city centres.Urban culture has become the legitimation for control.
Walter Christaller explained the location of urban cities in terms of their functions as service centres.The basic assumption was that a given rural area supports an urban centre which in turn serves the surrounding countryside. There are smaller towns for smaller areas and bigger cities for larger regions. This concept permitted Christaller to build up an integrated system of cities according to their size.
His views conceiving a city as a central place within a rural area was elaborated by Edward L.Ullman with considerable modifications. He admits the vulnerability of the scheme for larger places. In highly industrialized areas the central place schemes is generally distorted by industrial concentration in response to resources and transportation that it may be said to have little significance as an explanation for urban location and distribution.
Hyot in his sector theory talked about the growth of cities taking place in sectors and these sectors extend from the centre to periphery.
The concentric zone theory given by Park and Burgess suggested that modern cities consisted of a series of concentric zones. There are five such zones
Gans and Lewis through compositional theory hold that the composition of a city's population differs from that of a small town in terms of factors such as class, education, ethnicity and marital status.
Multiple Nuclie theory given by Harris and Ullman discuss that there is not one centre but several centers for the city. Each of the centers tend to specialize in a particular kind of activity-retailing, wholesaling, finance, recreation, education,government.Several centers may have existed from the beginning of the city or many have developed later in a division from one centre.
According to Castells to understand cities and urbanism one has to understand the process by which spatial forms are created and transformed. The architecture of cities expresses the struggles and conflicts between different groups in society. City is not only a distinct location but also as an integral part of processes of collective consumption.