In ancient geography, there is a set of theories to divide yin and yang, in which the yin of mountains and rivers refers to the north of mountains and the south of water, which is called yin. The south of the mountain is called Yang, and the north of the mountain is called Yin.
China lies in the northern hemisphere. The sun rises in the east and finally sets from the west through the south. Sunny in the south and sunny (sunny) in the north. The sunshine in the south of the mountain is bound to be more abundant than that in the north of the mountain, so the south of the mountain is called Yang and the north of the mountain is called Yin.
The topography of China is high in the northwest and low in the southeast. Rivers often flow to the southeast, and the south bank of the river is vulnerable to the impact and erosion of the river, forming a situation that the south is wet and the north is dry, so the water in the north is sunny and the water in the south is cloudy.