WRITING CAREFULLY: An elderly citizen fills in the questionnaire of the sixth national census at Beijing's Taiyangyuan Community on November 1 (ZHANG YU)

By the end of 2009, there were more than 17.5 million permanent residents in Beijing, among which more than 5 million were from other areas, according to official figures released in June.

As the places where they are registered and where they live are not the same, and since many people cannot always be tracked down, it is hard to do a census for the floating population, according to Gu.

Since people are more likely to be at home in the evening and on the weekend, census takers need to work until 9 p.m., Shang said. "We have also tried to choose a good time to visit, based on different lifestyles, and make appointments with people who seem absent for a long time."

Expats included

For the first time, foreigners living on the mainland were included in the census.

In order to get accurate information, millions of appointment letters had been delivered to those foreigners in Beijing before November 1, said Su Hui, Deputy Director of the Beijing Municipal Bureau of Statistics.

Yang Shu, an official with the Census Office of Maizidian, a multinational community in Beijing's Chaoyang District, said their office recruited volunteers with bilingual or multilingual skills to help with the census. They have also translated the questionnaire into at least five languages, including English, French and Japanese.

The questionnaire for foreigners is much easier and shorter compared to that for mainland residents.

"In fact, most foreigners are cooperative. They would answer my questions after I introduce myself as a census taker and some would even volunteer to help me contact their friends in the same community," said Li, who was responsible for a community with many foreigners.

"Of course, it's also difficult to find some of these foreigners, but we will try to reach every one of them by making repeated visits," Li said. "Furthermore, we will also leave notes on their doors suggesting they make an appointment with us."

Officials said foreigners living illegally in the country will not be repatriated as a result of information collected during the census.

In order to have more accurate figures, from November 11 to November 30, another round of census taking will be launched. One in 10,000 households will be visited again, with the National Bureau of Statistics sorting and filing the data through December.