I won’t completely disagree with this, however, a survey company typically will not want the liability of locating buried utility’s. They are almost always marked from the respective utility companies and with a specific color associated for the type of utility (blue=water, yellow=gas, red=electric, orange=communications). Also, If they are there for marking utilities they aren’t going to mark them outside of the “work zone” by too much of a margin because it’s not needed. So it goes to show how large the area could potentially be.