HALF the joy of walking-really enjoyable walking, not the sort where one reckons up the milestones with a stop-watch—lies in maps. Maps that show villages and inns and post offices and all the little lanes and bridle paths that motorists never see as they tear along their wide black roads. In his talk this evening Mr. Simpson will evoke some of the magic that lurks in every Ordnance map and even show how they can be used in fireside games.