Foundation
River Chart and Luo Writing河圖洛書
Two old number diagrams. One shows the elements producing each other, the other shows them controlling each other.
河出圖，洛出書，聖人則之。
Yi Zhuan, Xi Ci
河圖一六為水居北，二七為火居南，三八為木居東，四九為金居西，五十為土居中。
Xie Ji Bian Fang Shu, vol. 1
洛書戴九履一，左三右七，二四為肩，六八為足，五居中央。
Xie Ji Bian Fang Shu, vol. 1
What it is
The Xi Ci says the River gave a chart and the Luo gave a writing, and the sages followed them. Both show numbers as groups of dots. Odd numbers are yang and even numbers are yin.
River Chart
One and six sit in the north as water, two and seven in the south as fire, three and eight in the east as wood, four and nine in the west as metal, five and ten in the centre as earth.
Xie Ji Bian Fang Shu reads this as the order in which the elements produce each other.
Luo Writing
Nine is at the top and one at the bottom, three on the left and seven on the right. Two and four are the shoulders, six and eight the feet, and five the centre. Every row, column and diagonal adds up to fifteen.
Xie Ji Bian Fang Shu reads this as the order in which the elements control each other.
Where it is used
The Luo Writing is the base of the Nine Palaces. The River Chart’s pairs of one and six, two and seven, explain the Five Stem Unions.
Sources Xie Ji Bian Fang Shu, vols. 1, 2 and 8; Yi Zhuan.