Monitoring movement to and from the cities is one of the most vital tasks of the 2010 census to help urban and national planners.

The country's transient population hit 211 million at the end of last year and is expected to increase to 350 million by 2050, according to a June National Population and Family Planning Commission report.

More than half of Shanghai residents without a Shanghai hukou residency permit still hope to stay a long time, according to the latest annual report published by the Shanghai Population and Family Planning Commission on Thursday.

"We asked all non-local people to fill out the forms because the transient population has been growing fast over the last 10 years in China," Yu says.

"We need to figure out where people go and how the population is distributed exactly."

The main difference between this sixth national census and previous ones is the government has to make a "better plan" to handle a much more complicated situation, says Liu Huifeng, a professor at the Population Research Institute of Fudan University in Shanghai.

"Ten years ago, we didn't have such a large transient population and foreigners," says Liu, an official for the 1990 and 2000 censuses.

"But with the fast economic and social development, especially after the Beijing Olympics and Shanghai Expo, more and more people are moving around and foreigners are more often coming to the country."

Census figures are the official starting points for government plans to manage family planning, housing, education, health, public transport and unemployment, Liu explains.

"In short, it's a test for the country's development and openness," Liu says, "Everyone should take an active part."

Liu's message about the true meaning of the census has not failed to reach Lan Yan, a Chongqinger who's been living in Qiu's Shanghai residential compound more than 10 years.

"Our country is becoming stronger and more prosperous," she says. "It's good to do the census for better development."

Fast facts: Sixth census

The last census was 2000. Previous censuses were conducted in 1990, 1982, 1964 and 1953

"This will be the most challenging census we have ever encountered in history," says Yu Xuming, deputy director of the Shanghai Census Office

Preparations began two years ago and China is spending 8 billion yuan ($1.2 billion). Four million census-takers will knock on the doors of some 400 million Chinese mainland households to count some 1.4 billion people.

Participants fill out one of three forms: Nine out of 10 lucky Chinese mainlanders get a short form, but 10 percent fill out the long form, an official half-hour's work. Foreigners, Hong Kongers, Taiwan and Macao residents fill out their own form with name, gender, nationality and purpose for residing on the Chinese mainland.

Information pertaining to foreigners will be sent directly to central government officials. All information will be collected under privacy protection laws and will not be used for other interests. All original documents will be destroyed once details are transferred to a government database.

No penalties will be given to those who refuse to cooperate, Yu says, although participating in the census is strongly encouraged.

The key findings of the census will be made public by the National Statistics Bureau in April. Further summarizing and in depth analysis of data is expected to continue to 2013.