What is the difference between the holes at the camp and the holes outside the compound?

From the text:

Back at the compound, they had dug in a systematic order, row upon row, allowing space for the water truck. But out here there was no system. It was as if every once in a while, in a fit of frustration, the Warden would just pick a spot at random, and say, "What the hell, dig here." It was like trying to guess the winning numbers in a lottery.