I think that Gee evolved into Decca.. Similar lattice charts where accuracy deteriorated as one got further away from the transmitters. The information could be presented directly on special roller maps but the topography was distorted bordering on impossible at the edge of cover. A mainstay of the RAF SAR, North Sea Helicopters and the fishing fleet and also used in Viet Nam until the advent of GPS. At North Denes Heliport in the early days of gas exploration the single pilot used to radio his Decca readings back to the ops room and they would tell him where he was, which way to go, etc..