This Qing-dynasty atlas painted in color is formatted in accordion pleat-like leaves, in 21 folded sheets. The directions used in the maps are the exact opposite of those commonly used, that is, the south is on the top, the north at the bottom, the west is on the right side, and the east on the left. The maps illustrate the distribution of dykes along the Yellow River within the territory of Henan Province. The atlas starts from the west with Huayin Xian, which borders Shaanxi and Shanxi provinces, and continues eastward to Caodan Ting in Shandong Province and Xiaonan Ting in Jiangnan. The fortresses, dams, and numbers of soldiers and dam laborers along the tributaries of the Yellow River are listed in detail. The descriptions attest to the difficulty of regulating the river and the degree of distress that it sometimes imposed on the people living near its banks. The word sao in the title denotes a kind of material used in ancient times in river conservancy projects to protect the riverbanks and to block the mouths of rivers. It was made of 70 percent willow and 30 percent straw, tied together into bundles. Later, stalks of sorghum were also used. The bundles were stored for use in emergency. The word was also applied to name different kinds of laborers according to their tasks. Sometimes dykes made with such material were also called sao. Sao was discussed in detail in juan 11 of Meng xi bi tan (Jottings written by the Dream Stream), a work on natural science written by the Song author Shen Kuo (1031–95).