Proposals regarding Urban Agglomerations (UAs) forwarded by the State/UT Directorates of Census Operations are scrutinized and finalized in Social Studies division. In 1961 Census the concept of 'Town Group' was adopted to obtain a broad picture relating to urban spread. This was refined in 1971 with the concept of Urban Agglomeration to obtain better feedback in regard to urban contiguity, processes, trends of urbanization and other related matters. This concept remained operative in 1981, 1991, 2001, and in 2011 Censuses without any change or modification.
An Urban Agglomeration is a continuous urban spread constituting a town and its adjoining outgrowths (OGs), or two or more physically contiguous towns together with or without outgrowths of such towns. In some cases, railway colonies, university campuses, port areas, military camps, etc. would have come up near a statutory town outside its statutory limits but within the revenue limits of a village or villages contiguous to the town. Each of these individual areas may by itself not satisfy the criteria for it to qualify as an independent urban unit but may qualify to be clubbed with the existing towns as their continuous urban spread (i.e., an Outgrowth). For the purpose of identification of Urban Agglomerations following criteria are adopted:
(a) The core town or at least one of the constituent towns of an urban agglomeration should necessarily be a statutory town.
(b) The total population of an Urban Agglomeration (i.e., all the constituents put together) should not be less than 20,000 as per the Preceding Census.
In varying local conditions, there were similar other combinations which have been treated as urban agglomerations satisfying the basic condition of contiguity.