A list is a continuos hill. For sweet potatoes. about six inches high and 12- 13 inches widewith a trench between the lists. Today I use 36 inches between rows, but in my youth we used 42 inch spacing. When I was a kid we we ran them up with a two horse plow. When we got a tractor used a disk lister. To day I use a lister on the tiller, actually I use the Till-Row attachment.