KASHGAR, China — A God’s-eye view of Kashgar, an ancient city in western China, flashed onto a wall-size screen, with colorful icons marking police stations, checkpoints and the locations of recent security incidents. At the click of a mouse, a technician explained, the police can pull up live video from any surveillance camera or take a closer look at anyone passing through one of the thousands of checkpoints in the city.

To demonstrate, she showed how the system could retrieve the photo, home address and official identification number of a woman who had been stopped at a checkpoint on a major highway. The system sifted through billions of records, then displayed details of her education, family ties, links to an earlier case and recent visits to a hotel and an internet cafe.

The simulation, presented at an industry fair in China, offered a rare look at a system that now peers into nearly every corner of Xinjiang, the troubled region where Kashgar is located.

This is the vision of high-tech surveillance — precise, all-seeing, infallible — that China’s leaders are investing billions of dollars in every year, making Xinjiang an incubator for increasingly intrusive policing systems that could spread across the country and beyond.