It is closely related to over-urbanization of a city. Over a period of time, people from the OverUrbanized area start moving towards the fringe area around the cities. Such areas around the cities gradually start developing asan urban area. This phenomenon is known as Sub Urbanisation.
There are several factors which leads to the process of Sub-urbanisation such as :
1. High cost of living in over urbanized area,
2. Development of transport facility around the horizons of over urbanized area,
3. New Work culture that does not necessitate the physical presence on every day.
4. inclusion of surrounding areas of towns within its municipal limits.
Delhi is a typical example; wherein the all the above mentioned factors have led to the development of sub urbanized area. E.g. Ghaziabad, Faridabad, Meerut etc.