Why does geomantic omen say that one divination governs three mountains?

What exactly do the 24 directions of one divination governing three mountains and eight diagrams in Feng Shui mean?

Kangua: Sanshan stands for "no child is expensive" (due north) root melon: Sanshan stands for "ugly root shade" (northeast) real melon: Sanshan stands for "Jia Mao Yi" (due east) Yungua: Sanshan stands for "Chen Xun Si" (southeast) Starting from melon: representing "Jia Mao Yi"