In ancient times, the mountains in the south were sunny in the north, and the mountains in the north were cloudy in the south. "Shuibei Mountain is called Yang in the south, and Shuinan Mountain is called Yin in the north." The sunny side of the mountain is the south.
The dark side of water is the south.
contrary/opposite
The shady side of the mountain is north.
The front of the water is north.