2. Materials and methods
2.1 Study
area
China’s territory is vast, with a large north-south span, and is about
9.6\(\times 10^{6}\) km2. China has the complex and
diverse climate types, among which the continental monsoon climate is
prominent. Its annual precipitation decreases from southeast coast
regions to northwest inland regions. The elevation is high in the west
and low in the east, showing three ladder-like distributions in space.
Moreover, China boasts a diverse topography, with mountains, plateaus
and hills accounting for about 67%, and basins and plains accounting
for about 33%. In addition, China is the world’s most populous country,
the total population of which was 1,411.78 million by the end of 2020
according to the seventh national census. Among them, 63.89% of people
lived in urban areas, and the urban population proportion increased by
14.21% compared with 2010. The Hu Line, first proposed by Hu Huanyong,
also known as the “Heihe-Tengchong” Line. It was initially used to
demonstrate the population density differences of the areas either side
of the line, and later also proved to be the natural and ecological
boundary (Chen, 2016; Kong, 2022). In this paper, 368 cites in China
were chosen, and Taiwan Province, Hong Kong and Macau were excluded due
to the inaccessibility of data. To highlight regional differences in
urbanization and ecosystem health, the entire country was divided into
seven sub-regions: North China (NC), Northeast China (NE), East China
(EC), Central China (CC), South China (SC), Northwest China (NW), and
Southwest China (SW) (Fig 1).