If you are going to travel cross-country on foot, you need a map. Now there are different kinds of maps. One sort is the large-scale relief map, which marks all the paths, bogs, crags, and so on in detail. Since the walker needs the fullest information about his chosen route, he must have a map of that sort. But for choosing between the various ways he might go, he could well learn more, and more quickly, from a small-scale map that left out the detailed geography and just showed him the