India has begun the mammoth task of conducting a count of its billion plus population.
More than two and a half million census workers branched out throughout the vast nation on Wednesday to document details of all Indians.
The three-week phase of the census is the most challenging as it involves a physical count of the country's citizens. The mammoth exercise will be completed by the end of the month.
To ensure that every remote corner is accessed, census takers will be armed with satellite maps of the more than 600,000 villages in the country.
President Pratibha Patil was the first person to be visited by census officials. She appealed to people to assist in the vast task they are undertaking.
"Please take part in the census which is being conducted by our country and which is on an enormous scale," Patil said. "Please take it as your national duty, because it is in your interest and in the interest of our nation."
This year's census, which includes details of income, religion, and education, is more exhaustive than previous ones. For example, it will involve finding out whether people live in mud huts or concrete structures and whether they have access to piped water, electricity and toilets.
Census enumerators will not only knock on doors of every house. In a country where many are still poor and homeless, on the evening of February 28 officials will count those who spend the night sleeping on pavements or under bridges.
For the first time, officials will also collect fingerprints and photograph every resident of the country. Called the biggest project of its kind in modern history, officials say this data will be used to give citizens biometric identity cards and compile a new National Population Register.
The census is conducted every ten years. It is a complex task in a vast country with great geographical, cultural and linguistic diversity. Census officials have already listed the number of households in India and estimated the population at 1.17 billion.
Officials say the census helps them in making new policies, seeing whether government programs are effective and identifying areas and communities which may need assistance.
India has conducted a census every 10 years since 1872. Census officials proudly say the task has been done for over a century despite all problems such as drought or war.