Heihe-Tengchong Line

The Heihe–Tengchong Line (simplified Chinese: 黑河-腾冲线; traditional Chinese: 黑河-騰衝線; pinyin: Hēihé-Téngchōng xiàn), also called the Aihui-Tengchong Line (and internationally as the Hu line) is an imaginary line that divides the area of China into two roughly equal parts. It stretches from the city of Heihe to Tengchong County, diagonally across China.

Chinese population geographer Hu Huanyong imagined the line in 1935 and called it a "geo-demographic demarcation line". As this line was proposed in 1935, the map of China would have included Mongolia but excluded Taiwan.

This imaginary line divides the territory of China as follows (going by 1935 statistics):

Despite an epic urban migration, 2002 and 2015 statistics remain nearly identical vis-à-vis the line:

The minor change in total population percent from 1935 to 2015 is attributed to Han Chinese migration to urban areas in the autonomous regions of Tibet and Xinjiang, as well as one-child policy restrictions on the majority, with exceptions for largely-minority groups west of the line. However, during the 2000-2015 period, population in the west of the line indeed grew faster than the east, but the growth wasn't sufficient to budge the rounded percentages. Most of this growth was contained in the cities of Ürümqi, Lanzhou, Ordos, and Yinchuan, although some tribal non-city areas also registered high growth. After 80 years, the area west of the Heihe–Tengchong Line remains relatively rural, rugged or inhospitable, underdeveloped and poor as compared to the east.

...
Wikipedia