Geographically speaking, the world's deserts are distributed in 13 regions (William G.Mc.G. Deserts of the world,1970), and the deserts which caused by climatic factors are concentrated in North and South latitude between 15 ° -35 ° (Figure 4-5). The deserts in southern hemisphere are starting from the Kalahari and Namib Desert along the Atlantic coast, passing the Indian Ocean, going through the Australian desert, and crossing the Pacific to the Salar desert in South America; and the deserts in northern hemisphere are starting from the Sahara desert along the Atlantic coast, crossing the Suez canals, going over the Red Sea, passing the Arabian desert, going through Iran, Afghanistan, the India Thar Desert, crossing the Pacific, and finally arrive in southwestern North America.

The deserts formed by topographic factors are mostly located in the north latitude between 35 ° -50 °, and concentrated in central Asia and western United States. The area of deserts in China accounts for 6.3% of land area (Figure4-6), and the deserts are mainly located in north latitude between 37 ° -43 °. Taklamakan Desert is the largest desert of China.(Figur4-7).

Figure 4-5 The distribution of world desert (After Nathanie Harris,2003)

Figure 4-6 The distribution of China desert

 Figure 4-7 The area of main deserts in China(After Wu Zheng, 1982)