At the end of the first Dune book, the Paul Atreides and the Fremen attack Arrakeen. They bring down part of the Shield Wall using Atomics in order to be able to ride worms to the city. I tried to find the exact location of the breach but did not find an exact location.
I think there are four locations that are probable as there, the Shield Wall is the thinnest. IMO, the most probable would be red. On the other hand, it's rather close to Arrakeen and with the convention on atomics, it could be risky to blow up an atomic bomb this close to Arrakeen, also considering radiation. Green would probably be less desirable, as you have to blow up to different parts of the wall.
Blue and purple are equal, far away from population (and therefore not in such a big risk of breaking the convention) but it greatly increases travel time from the breach to Arrakeen.
From the book:
Paul nodded, kept his eye on the time-standard dial in front of the signalman. Presently, Paul looked at Gurney, raised a hand, returned his attention to the dial. The time counter crawled around its final circuit.
"Now!" Paul shouted, and dropped his hand.
Gurney depressed the blast trigger.
It seemed that a full second passed before they felt the ground beneath them ripple and shake. A rumbling sound was added to the storm's roar.
The Fedaykin watcher from the telescope appeared beside Paul, the telescope clutched under one arm. "The Shield Wall is breached, Muad'Dib!" he shouted. "The storm is on them and our gunners already are firing."
For the watcher to be able to observe that the gunners are firing at Arrakeen, I don't see another way than being close to red. Is my argument correct and has it ever been clearly described / shown at which location the Shield Wall was breached?