What is He Tu? (河图)

The entire branch of Chinese Metaphysics is a subset of Yi Jing. In the previous Yi Jing article, we understand how things around us are derived from Taiji. But the evolution does not stop there, here we come to one of the important diagram in Chinese Metaphysics. This pictorialpresented is one of the major backbone system in Chinese Metaphysics:
He Tu. (河图)