India is kicking off an unprecedented effort to enumerate 1.2 billion people. The count is also meant to gather data for an equally ambitious project to give every Indian a unique identification card.
The number of Indian census takers alone - 2.5 million - outnumbers the entire population of some small countries. They will be fanning out across what is the world's seventh largest and second most populous nation.
Home Minister Palaniappan Chidabaram calls the task unprecedented. He is appealing to everyone in India to voluntarily participate. "An exercise of this kind has not been attempted anywhere else in the world. This exercise must succeed. This exercise will succeed. But we need your cooperation and support," said Chidabaram.
The first census taker for the once-every-decade count showed up at the presidential palace to start the initial process, known as "house-listing."
President Pratibha Patil was the first person out of an estimated 1.2 billion to be counted.
The census takers will record such details as what peoples' houses are made of, whether they have toilets and access to drinking water and even if they have a mobile telephone or an Internet connection. To try to count everyone, they are supposed to venture into such hazardous places as remote forests under the control of rebel Maoists.
The census takers are also required to tabulate the homeless wherever they can find them, such as on railway platforms and under bridges.
For the first time, everyone who is registered will be photographed and fingerprinted. That data will be used to issue national identity cards, in the next several years. The cards are supposed to help the poor, who may have no other means of identification to open bank accounts and to obtain government benefits. Government officials say the cards will cut fraud. But privacy advocates are raising concerns, arguing that the program could give rise to intrusive government surveillance of citizens.
India's census-taking tradition dates back to the British colonial era, when the first enumeration was conducted in 1872. Since then it has been conducted about once every decade.