The Chinese tradition attaches a great importance to two complementary principles known as yin and yang and brought together in the symbol carrying the same name. Yang depicts the light or the white half of the symbol and yin the darkness or the black half. The way yin and yang interact within this common representation is derived from the double spiral drawing separating the white and black halves of the symbol and the orientation mode adopted in China at different eras.
The yin-yang symbol depicts the most perfect representation of the balance between yang and yin, white and black, warm and cold, light and darkness, day and night, Sun and Moon, Heaven and Earth… It follows that the components, mainly material, of the world can be arranged into two categories associated with two principles: yang including all what is linked to light, essence and actuality; yin covering their opposites, darkness, substance and potentiality.
However, the light illuminating the world is not completely deprived of shade and darkness of clearness. Therefore, the presence of the black and white spots in the white and black halves of the yin-yang symbol. In fact, yang and yin recover more complementary than opposite categories. It should not be forgotten that these two principles take their source in the primeval Unit which gives rise to the primeval polarization, Heaven-Earth. If Heaven is completely yang and Earth entirely yin, the other polarities, made of complements, combine yang and yin. There is no yang without yin nor yin without yang. Their natures are strongly interwoven and both contribute to the dynamics of the Chinese tradition, which is far away from the static presentations describing it.
When the yin-yang symbol is represented vertically, yang is dominating yin as Heaven is always “above” Earth. When it is represented horizontally, yang and yin are constantly exchanging their influences and none of them can prevail in the long run. In this case, the clear and dark areas of the yin-yang symbol can lay one over the other without any dominance by one of them.
Put into parallel with cardinal points, yang can only be associated with light, i.e. to South or East. Similarly, yin is necessarily related to darkness, i.e. to North or West. The Chinese tradition mostly favours the solar orientation where the being faced South and gave preference to the left or East. That is why, the ancient Chinese cartographic representations are generally, but not always, putting South at the “top” and North at the “bottom” unlike our contemporary representations.