As per the Census of India 2011, 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.
An Urban Agglomeration must consist of at least one statutory town and its total population (i.e., all the constituents put together) should not be less than 20,000 as per the 2001 Census. In varying local conditions, there were similar other combinations that have been treated as urban agglomerations satisfying the basic condition of contiguity.
Examples: Greater Mumbai UA, Delhi UA, etc.