Back when I started, we dug in straight lines no matter what. One summer, our yield dropped hard in a rocky area. I got tired of hitting the same snags and switched to a zigzag path on a hunch. It let the cutter head break up the bottom without getting stuck. We pulled up twice the material that week. Now I map out the tough spots first. Sometimes the old way just needs a tweak.
Your suggestion to map rocky zones first has merit, but it can lead to missing other important details. A full survey often catches issues that isolated mapping misses. Starting with a broad overview tends to work better.