India is launching a new census in which every person aged over 15 will be photographed and fingerprinted to create a biometric national database.
The government will then use the information to issue identity cards.
Officials will spend a year classifying India's population of around 1.2 billion people according to gender, religion, occupation and education.
The exercise, conducted every 10 years, faces big challenges, not least India's vast area and diversity of cultures.
Census officials must also contend with high levels of illiteracy and insurgencies by Maoists and other rebels in parts of the country.
President Pratibha Patil was the first person to be listed, and appealed to fellow Indians to follow her example "for the good of the nation".
"Everyone must participate and make it successful," she said in Delhi.
'Unstoppable'
This is India's 15th census and the first time a biometric element has been included.
"India has been conducting a national census since 1872," the man leading the exercise C Chandramouli told the AFP news agency. "Nothing - floods, droughts, even wars - has been able to stop it.
"The trick is to get things right the first time. There is no question of a re-census."
Over the next year, some 2.5 million census officials will visit households in more than 7,000 towns and 600,000 villages.
They will first begin the process of house listing - which records information on homes. This count will, for the first time, also attempt to gather information on the use of the internet and the availability of drinking water and toilets in households.
The physical count of residents will take place from 9-28 February 2011.
The mammoth registration exercise will stretch over 11 months, consume more than 11 million tonnes of paper, and cost 60bn rupees ($1.3bn; £880m).
India's Home Minister, P Chidambaram, has described the process as the biggest of its kind in human history.
"An exercise of this kind has not been attempted anywhere else in the world," he told reporters in the capital.
The national census is the only source of primary and credible data in India and is used not just to formulate government policies but also by private companies to identify markets for their products, says the BBC's Sanjoy Majumder in Delhi.
The first 16-digit identity numbers are due to be issued starting in November.
The full census results will be released in mid-2011.
The collation of biometric information on a national database raises questions about possible infringement of civil liberties in the future.
BBC correspondents say many Indians appear to support the new ID cards, believing it will make it easier to receive things like state benefits.
The government will then use the information to issue identity cards.
Officials will spend a year classifying India's population of around 1.2 billion people according to gender, religion, occupation and education.
The exercise, conducted every 10 years, faces big challenges, not least India's vast area and diversity of cultures.
Census officials must also contend with high levels of illiteracy and insurgencies by Maoists and other rebels in parts of the country.
President Pratibha Patil was the first person to be listed, and appealed to fellow Indians to follow her example "for the good of the nation".
"Everyone must participate and make it successful," she said in Delhi.
'Unstoppable'
This is India's 15th census and the first time a biometric element has been included.
"India has been conducting a national census since 1872," the man leading the exercise C Chandramouli told the AFP news agency. "Nothing - floods, droughts, even wars - has been able to stop it.
"The trick is to get things right the first time. There is no question of a re-census."
Over the next year, some 2.5 million census officials will visit households in more than 7,000 towns and 600,000 villages.
They will first begin the process of house listing - which records information on homes. This count will, for the first time, also attempt to gather information on the use of the internet and the availability of drinking water and toilets in households.
The physical count of residents will take place from 9-28 February 2011.
The mammoth registration exercise will stretch over 11 months, consume more than 11 million tonnes of paper, and cost 60bn rupees ($1.3bn; £880m).
India's Home Minister, P Chidambaram, has described the process as the biggest of its kind in human history.
"An exercise of this kind has not been attempted anywhere else in the world," he told reporters in the capital.
The national census is the only source of primary and credible data in India and is used not just to formulate government policies but also by private companies to identify markets for their products, says the BBC's Sanjoy Majumder in Delhi.
The first 16-digit identity numbers are due to be issued starting in November.
The full census results will be released in mid-2011.
The collation of biometric information on a national database raises questions about possible infringement of civil liberties in the future.
BBC correspondents say many Indians appear to support the new ID cards, believing it will make it easier to receive things like state benefits.
