Before-Heaven Bagua: The original form, said to come from markings on a tortoise shell, shows each element with its opposite (yinyang). The symbols are from the I-Ching (Yijing).
Probably the best-known diagram in Chinese culture is the Bagua. The Bagua (ba gua literally means "eight ways" or "eight directions") is one of the oldest forms in this Chinese tradition. Its earliest form dates back almost 5,000 years. It is the foundation of the I Ching (Yijing), or Book of Changes. It is considered to be a symbol of good luck, and eight is the luckiest number.
The earlier "Before Heaven" form of the diagram shows each of eight elements arranged opposed to its opposite. Today this form is most commonly associated with various schools of Tai Chi. It is also closely associated with Taoism. This is the form that Sun Tzu used in designing his system. All the elements in the "Before Heaven" form—heaven, earth, fire, water, lake, mountain, wood, thunder—are used either directly or as symbols in the text.
The After-Heaven Bagua are an unbalanced arrangement of the same elements. This arrangement is meant to reflect the dynamic universe.
Today, the Bagua is best known in its "After Heaven" form from Feng Shui, the Chinese art of creating harmonious living spaces. From this, you can see how positions have changed. Though it has many forms, the basic purpose of the Bagua is to show relationships between natural elements. In Feng Shui, these Bagua relationships include colors and areas of your life such as career, marriage, wealth, children, and so on. The eight sides also connect with eight trigrams (of the 64) in the I Ching.