Figure 1.

Pilot cities and unpiloted cities of circular economy in China. Note: the Heihe-Tengchong Line was proposed by Chinese geographer Hu [33] and is a demarcation line of population density extending from Heihe in Heilongjiang province to Tengchong in Yunnan province, from the northeast to the southwest of China. Its formation and development are closely related to natural conditions such as terrain, landform, climate, hydrology, and other factors correlated closely with social, economic, and human activities.