Urbanisation was the most significant between 1991 and 2001: data
Nearly half the population of Tamil Nadu live in urban areas, as the State continues to maintain its status as one of the country's most urbanised ones.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/nearly-half-population-state-live-urban-areas
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/hindu-chennai
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/tamil-nadu
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/urbanisation
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/population
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/census-2011
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/chennai-t
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/kanniyakumari
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/coimbatore-d
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/kanchipuram-d