There is no common global definition of what constitutes an urban settlement. As a result, the urban definition employed by national statistical offices varies widely across countries, and in some cases has changed over time within a country. The criteria for classifying an area as urban may be based on one or a combination of characteristics, such as: a minimum population threshold; population density; proportion employed in non-agricultural sectors; the presence of infrastructure such as paved roads, electricity, piped water or sewers; and the presence of education or health services. In this section, we will discuss different definitions and processes s associated with the urbanisation. It includes Census definition of Urban areas, Urban Agglomeration, OverUrbanization, Sub Urbanization, Counter Urbanization and Census towns.

In 1961 census, 'town' was defined and determined on the basis of number of empirical tests:

• a minimum population of 5000
• a density of not less than 1,000 per square mile,
• three-fourth of the occupations of the working population should be outside of agriculture.
• the place should have a few characteristics and amenities such as newly founded industrial areas, large housing settlements and places of tourist importance and civic amenities.

Urban Agglomeration

This term was introduced in 1971 census. Very often large railway colonies, university campuses, port areas, military camps etc. come up outside the statutory limits of the city or town but adjoining it. Such areas may not themselves qualify to be treated as towns but if they form a continuous spread with the adjoining town, it would be realistic to treat them as urban. Such settlement has been termed as outgrowths, and may cover a whole village, or part of a village. Such towns together with their outgrowths have been treated as one urban unit and
called 'urban agglomeration'.

Over-Urbanization

It refers to the increased exemplifications of the characters of urbanization in a city or its surrounding rural area. It results from excessive development of urban traits. Due to the expansion of the range of urban activities and occupations, greater influx of secondary functions like industry, increasing and widespread development of an intricate bureaucratic administrative network, the increased sophistication and mechanization of life and the influx of urban characters into the surrounding rural area, over urbanization gradually replaces the rural and traditionalistic traits of a community. Mumbai and Kolkata are two such examples of cities.

Sub-Urbanization

It is closely related to over-urbanization of a city. When cities get over-crowded by population, it may result in sub-urbanization. Delhi is a typical example. Sub-urbanization means urbanization of rural areas around the cities characterized by the following features:
• a sharp increase in the ‘urban (non-agricultural) uses’ of land
• inclusion of surrounding areas of towns within its municipal limits, and
• intensive communication of all types between town and its surrounding areas

Counter-Urbanization

It is a demographic and social process whereby people move from urban areas to rural areas. It first took place as a reaction to inner-city deprivation and overcrowding. Counter urbanization occurs when some large cities reach a point where they stop growing further or actually begin to decrease in size as their population start moving into suburban areas or smaller cities thereby leapfrogging the rural-urban fringe. There are instances which show that the
phenomenon of counter urbanization is occurring in India.

Census Towns

In 2011, a new definition of census town has been developed. This urban classification of 'census towns' helps differentiate between India's small farming communities and the larger market town-type settlements that are experiencing rapid and haphazard growth.
To be classified as a census town, a village must fulfil three criteria;
• it need at least 5,000 inhabitants,
• a density of 400 people per sq. km, and
• at least three quarters of its male working population must be "engaged in non-agricultural pursuits".