Eighty years after Chinese geographer Hu Huanyong drew a line to separate the sparsely populated northwest of China from the densely populated southeast, a remote-sensing report observed significant population density growth in the west.

The original line cut through central China, connecting Hehei in northeastern China's Heilongjiang province with Tengchong in southwestern China's Yunnan province. In 1935, when the line was marked, some 5.61 percent of the Chinese population lived in 56.29 percent of the territories in northwest China, while 94.29 percent lived east of the line.

Between 1935 and 2010, the average population density in the west grew from two persons per square meter to 16 persons; in the east, that figure rose from 107 to 303, according to the report on China's sustainable development, issued by the Chinese Academy of Sciences.

In the buffer zone spreading 300 to 500 kilometers from either side of the line, the

natural wetlands had shrunk by 11.8 percent in 2015 from their size in the 1980s, and forest cover was down by 3.8 percent. In the same period, land for construction or farming expanded by 32.4 percent. The construction rate was higher in northwestern China than in the southeast, the report noted.