When those charged with carrying out history's largest census arrive in this squalid migrant labourers' settlement south of Beijing, they may find it hard to get an accurate count of anything.
The muddy alleyways off Laosanyu Road teem with thousands of men, women and children, all of them from somewhere else, usually the country's vast and largely impoverished rural interior. Many have lived in and around Beijing for years or even decades; others count their time here in months or days.
The "farmer-workers," as they are known in Chinese, are at once the engine of this country's rapid economic growth, and those it has left behind. And no one knows for certain just how many of them there are.
More than six million people - a number almost three times the size of the People's Liberation Army, and larger than the population of Denmark - will on Monday fan out across this country's 31 provinces to begin China's first national census in a decade. Though a population survey carried out at the end of last year estimated the population of the People's Republic of China at 1.334 billion, there are far too many unknowns for that number to be considered definitive. Some demographers believe the real number of Chinese may be closer to 1.5 billion.
There are several reasons China's government has a poor handle on the number of people it rules, but the biggest one is that the country is in the midst of the world's biggest-ever peacetime migration. Over the past three decades, hundreds of millions of rural Chinese have flocked to the cities in search of work and better lives. Estimates of the number of migrant workers and their families range from 130 million to more than 200 million. To find the real number will mean going door-to-door in villages such as Daxing, and asking those who live here to tell the truth, even when it could have uncertain consequences.
"The number of people living here changes all the time," said Xu Yingyun, who is raising her six-year-old grandson in two small rooms the family rents at the end of one of Daxing's many alleys. She said the family had no idea who their neighbours currently are, since the other residents frequently change, with many staying only as long as their latest job lasts before moving on to another district or city.
The numbers are imprecise because China's hukou household registration system restricts where people can live and work, forcing migrants to live in the shadows of places such as Beijing, Shanghai and Guangzhou. An unknown number - believed to be in the millions - have had second or third children in violation of the country's once-child population control laws. While their parents are registered in the wrong place, the children often aren't registered at all, leaving them without the necessary documentation to even attend school.
Hoping to remove the asterisk that has long accompanied their country's population counts, China's government plans to marry a physical head count with their own population registry for the first time, with the in-person count taking precedence wherever there is a conflict. To encourage migrants to be honest about how and where they live, the government has mixed a massive propaganda campaign - green banners around the country urge citizens to "co-operate fully to reconcile household and population records" - with a promise of reduced fines for those who admit hukou violations or reveal their extra children to the census-takers.
"Our enumerators will go anywhere that there are people to register," said Fang Nailin, the vice-director of the census. "Within each block, we will not miss any building. Within each building, we will not miss any household. Within each household, we will not miss any individual. And with each individual, we will make sure they fill out each item [on the census questionnaire]"