The next census of India in 2012 - the gigantic exercise to determine the population of the country - will be a "digital census", with a mobile app used to collect data, Union Home Minister Amit Shah said today. He also proposed the idea of a multipurpose ID card for every citizen which includes passport, Aaadhar and the voter card. India's last census was carried out in 2011 when the country's population stood at 121 crore. Census 2021 will be the world's largest enumeration exercise, an official had said.