The Classic of the Green Bag, an early Han dynasty text, lays the foundational principles of feng shui. It concisely explains the relationship between celestial bodies and terrestrial forms, emphasizing the interaction of yin and yang energies. The text establishes the importance of analyzing landforms (luan tou) and qi flow (li qi) to achieve harmony and prosperity. Through metaphorical descriptions of celestial constellations and earthly geography, it illustrates the interconnectedness of heaven and earth and the impact on human affairs. The core concept is that the balance of these forces, reflected in the landscape, influences human well-being.