India on Thursday launches the task of counting its teeming billion-plus population, with 2.5 million people set to fan out over the chaotic south Asian giant to begin work for the 2011 census.
The exercise has formidable challenges -- coverage of a vast geographical area, left-wing rebels and separatists, widespread illiteracy, and people with a bewildering diversity of cultures, languages and customs.
"The census is a means of evaluating once in every 10 years, in a dispassionate manner, whether government programmes are reaching their intended target and plan for the future," Census Commissioner C Chandramouli told AFP.
Adding to the complexity of counting and classifying the world's second biggest population will be a simultaneous process of collecting biometric data on every person, to be used in a new National Population Register.
"It is also a challenge to see that the 2.5 million enumerators carry out the instructions we have given them without error," Chandramouli said from his New Delhi office.
Officials will collect fingerprints and photograph every resident for the first time for the register -- a process described by Home Minister P Chidambaram as "the biggest exercise... since humankind came into existence."
Along with census details, "personal attributes" will be recorded, such as declared nationality and marital status, and details on the proportion of bank account holders and cellphone users.
The twin census and population register processes will stretch over 11 months, consume 11.63 million tonnes of paper and cost 60 billion rupees (1.25 billion dollars).
"India has been conducting national census since 1872," said Chandramouli. "Nothing -- floods, droughts, even wars -- has been able to stop it."
The basic census will start with officials visiting President Pratibha Patil for her signature during the first leg of the process called "houselisting."
"Enumerators" will then fan out over the country to begin houselisting, which records information on homes, such as the construction material used or the availability of electricity and water.
The physical count of residents will be made between February 9-28 next year and the completed census will be released by mid-2011.
"The trick is to get things right the first time. There is no question of a re-census," Chandramouli said.
This time, to minimise the 2.3-per cent margin of error recorded in the 2001 census, officials will be armed with satellite maps of India's 608,786 villages.
"I have instructed enumerators to ensure they reach out to the women, the elderly, the disabled, nomadic communities and migrants -- usually left out in the census process," said Chandramouli.
But Ashish Bose, a retired professor of Indian and Asian population studies at Delhi University, warned of mistakes creeping in despite the best efforts.
"Uneducated people in villages never know their ages correctly. It is never a '51' it always 50 or 55. But overall we conduct a good census -- no doubt about it and the vast majority of people are keen to participate," he said.
S Parasuraman, a demography professor at the Tata Institute of the Social Sciences in Mumbai, said the new population registry will provide a valuable database.
"In a disaster for instance, one will be able to pinpoint how many people were living at a place before and after the catastrophe struck. It will be a compilation of useful information enabling proper governance," he said.
Data collected for the National Population Register will in turn facilitate the issue of the 16-digit Unique Identity Numbers to all residents.
This will serve as a one-stop proof for all Indians to establish their identity, eliminating the current need to produce multiple personal documents.
The first identity numbers are expected to be issued by November this year.