In The World of Crop Dusting, Category A would be you flying from Bubbas Ranch over to a sourgum filed to spray. You would recognize the field by the color of the mud kicked up when your wheels skipped along. You would only be able to see the flagman from 1200 feet and would also be so low that you would only see him when he dove into a ditch to avoid you hitting him. He would be further confused as you are flying a Biplane and he could only see one wing as the upper is in the clouds....
Upon return you could tell where you had been by the types of wires wrapped around the main gear and Old Maudes phone line off the tail wheel
Thats sort of Cat A....