String walking is a very old method of aiming that alot of people use for NFAA type tournaments, where the yardage is known. The difference between string walking and gap shooting is: String walking, the point of arrow is held dead on each shot and the finger position on the string is moved up and down. with gap shooting, the point of arow is moved up or down and the hand position stays the same. I am not an expert on either method since i shoot instinctive, and I am sure there is alot more to it than that, but this is basically how it works.