In the chapter on terrain Sun Tzu spoke of six kinds of ground. Now, in the chapter on the nine grounds, he widens the scope to the situations that arise between one state and another.
The same army and the same soldiers must move differently when the position they are in differs. Sun Tzu divided those situations into nine.
用兵之法：有散地，有輕地，有爭地，有交地，有衢地，有重地，有圮地，有圍地，有死地
yong bing zhi fa, you san di, you qing di, you zheng di, you jiao di, you qu di, you zhong di, you pi di, you wei di, you si di
In the use of troops there is scattering ground, light ground, contested ground, open ground, crossroads ground, heavy ground, difficult ground, enclosed ground and death ground. (The Art of War, Nine Grounds, translated directly)