Hunched over a clipboard, squinting in the pale yellow glow of a street camp, Shika Shrivasta surveyed the grimy, wiggly boy in front of her.
"Address?" she asked, and he gestured vaguely at the park around them. She frowned at her papers: runaway nine-year-olds, jittery from solvent sniffing, do not have a category in India's census.
But the pair made their way through the form - the boy, Vishnu, doesn't work or go to school - until they were done and Ms. Shrivasta waved him on, turning with a sigh to the next homeless person sleeping rough on the streets of central Delhi.
"Everyone," she repeated through slightly clenched teeth, "has to be counted."
India concluded its national census this week, having tallied up some 1.2 billion souls, and the last night of counting focused on homeless people - of whom there are an estimated 150,000 in Delhi alone. Getting them into the count was just one in an array of staggering challenges: how to enumerate in the dozen areas under control of various armed rebel movements, and in the 572 tiny islands that make up Andaman and Nicobar; how to train 2.5 million enumerators and handle answers in 6,661 languages.
"In the developed world, you have a tremendous advantage, where you can post out the census form and people fill it up and mail it back," said C. Chandramouli, India's registrar general and census commissioner. "Here, census is a human drama."
It is also a window into how India is changing.
This census, for example, allows a respondent to list a gender of male, female or "other" - part of a growing acceptance of transgendered people.
There is a series of questions on mental and physical disability, which Mr. Chandramouli said has likely been sharply underreported in the past because of stigma.
There is also, for the first time, a question about divorce (in the past "divorced" and "separated" were one category) since anecdotal evidence suggests that many more married people separate than formally divorce. "We will see. Does anyone actually do the [divorce]process? And then it will be for the legal system to work out if the system is too difficult," the commissioner said.
The census attempts to collect some data on fertility, asking women not only how many children they have living, but also how many they have ever given birth to. However, only women who say they are now or have been married are asked about children; there is no question about births out of wedlock, although originally the registry office had planned to collect that data.
"When we field tested the question, we found the enumerators were not asking at the household itself, but going to the next house and then saying, 'I know you do not have such people in your family, but what about at that house?' " Mr. Chandramouli said. "You have to hand it to them for innovation - if I put the question on, they will get an answer for me."
Census results may help evaluate the impact of the massive social welfare programs undertaken by India's ruling Congress Party in recent years. A huge investment in universal primary education may be reflected in higher literacy rates or higher reported school enrolment. (Or it may not: Critics, who say the program has foundered on a lack of skilled teachers and poor planning, may be vindicated by the results.)
And the rural employment guarantee scheme, the world's largest public works initiative with an annual budget of about $10-billion (Canadian), may be responsible for a drop in the number of people who report having worked for at least a few months in the past year, or who say they migrated for economic reasons.
A critical piece of data will be the number of women compared to men - India's sex ratios have been declining steadily for the past three decades, as a strong social preference for sons and smaller family sizes encourages sex-selective abortion. Government policies have been aimed at discouraging the practice, but population sampling indicates those campaigns have had no impact. It will be a sharp embarrassment for the central government if, as predicted, the sex ratio is found to have fallen even further over the past decade since the last census.
The toughest question involves age, split into two parts: "How old are you?" and "When were you born?" Most Indians don't have an answer for either and the tendency is to round to the nearest zero or five, Mr. Chandramouli said.
For people who have no idea, enumerators prompt with key historical events, such as: "Were you born around the time of independence?" That can be further narrowed by asking: "Was it near this or that festival?"
"And then you get a month, more or less," Mr. Chandramouli said.
People are not asked about income, notoriously underreported here to evade a weak taxation system. Mr. Chandramouli pointed out that any income data collected would be so suspect as to be useless.
And the census does not ask about the most sensitive of Indian subjects, caste, to be addressed in a separate census in June. Demographers argued that including it in this census would prompt people to inflate numbers, because a percentage of jobs, school places and government seats are all reserved for low-caste groups, and thus ruin the integrity of the data. But with so much government policy based on remediating caste-based inequity, they agreed it was critical to collect the data.
Historical texts make reference to population counts done here as early as 800 B.C. The British began a formal census in 1872. Before this census, it took staff eight years to process and release data - barely time to catch their breath before the next one. But new data-capturing technology is currently scanning 1.5 million forms a day, Mr. Chandramouli said, and the bulk of the results from this count should be out by 2013.
While the Maoist territory, the homeless people, and the coding of 3,000 religions are an evident challenge, The commissioner's biggest headache is counting citizens in India's booming cities. In a village, everyone knows the teacher (all enumerators are teachers) and has time to sit and talk things through. But in the cities, people don't even know their neighbours. In upscale neighbourhoods, enumerators must battle their way through a maze of streets, seek out oddly placed gates or doors, talk their way past security guards and housekeepers, to get to a resident. "And then they say, 'Come back later, I'm off to yoga class or shopping.' "
India, in numbers
Enumerators needed for India's 15th national census.
Number of languages in which answers were delivered.
Estimated number of people counted.
It will take two years to process the bulk of results.