Yin and yang as, respectively, earth (the mountain growing to heaven) and heaven (the Big Dipper/Great Chariot which represents the order of the universal God), analogies used in Chinese common religion. The yang (heavenly) element in yin (earth) is here represented as a square signifying an "earth according to the order of heaven", while the yin (earthly) element in yang (heaven) is represented as a circle.
Own work
Aethelwolf Emsworth.