Locating some of the sites that either he himself, or friends of his, had visited was easy. The majority of the sites, however, had to be located with the help of satellite maps. As an engineer doing work related to city planning in a government-sponsored institution in Ju'nan county, Shandong province, Yuan is good at using satellite maps in his daily work.

For example, when he tried to locate the tomb of Zhao Ju, a foster daughter of Zhang Lu, a warlord of the late Eastern Han Dynasty, he first scoured history books to find out the basic area in which it should be located－Hongmiaoliang village, Mianxian county, Shaanxi province－where there should be a memorial temple and a tomb.

He remembered watching a documentary which mentioned Mianxian, and especially highlighted bandenglong, a local dance that is listed as a provincial-level intangible cultural heritage. When he watched the documentary again, he saw people performing bandenglong just in front of a temple that was located next to a tomb. After comparing the video with descriptions he found in books and online, he figured that it must be the tomb that he was looking for. After checking the satellite map, he found the site and was able to label it.

"To identify the locations, I often need to search a lot of material," says Yuan.

"Sometimes, when I visit some sites, Yuan asked me to give him my accurate longitude and latitude," explains Cheng. "At first, I didn't understand why he was so strict with the numbers, but later I learned that a minor difference in numbers could, in reality, point to another, more distant, place from the site, especially in mountainous areas.

"Yuan's efforts bring a lot of convenience for those who want to visit these sites," Cheng adds.