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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 with contrasting population densities. It stretches from the city of Heihe in northeast to Tengchong in south, diagonally across China. The eastern half, area shown in red in the map, is further subdivided into north and south halves.
As of 2015, 94% of China's population live east of the line, in 43% of its area, whereas 57% of the area of the country is west of the line, but only 6% of the population.
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 at the time included Mongolia (whose independence China did not recognise until after WWII) but excluded Taiwan (which was part of Japan at the time).
This imaginary line divides the territory of China as follows (going by 1935 statistics):
- West of the line (including Mongolia): 64% of the area, but only 4% of the population (1935)
- East of the line: 36% of the area, but 96% of the population (1935)
2002 and 2015 statistics
Despite a large scale urban migration mainly towards coasts but also trending south, 2002 and 2015 statistics remain nearly identical vis-à-vis the line:
- West of the line: 57% of the area, but only 6% of the population (2002)
- East of the line: 43% of the area, but 94% of the population (2002)
The major change in area between 1935 to 2015 is attributed to the acknowledge of the independence of Mongolia by China after the Yalta Conference. 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. 
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- Qinling–Huaihe Line, further subdivides eastern China in northern and southern halves