Art, said Picasso, is a lie that makes us realize the truth. So is a map. We do not usually (36) the precise work of the mapmaker with a (37) object of art. Yet a map has many qualities that a painting or a poem has. It is truth realized in a (38) way, holding meanings it does not express on the surface. And like work of art, it requires (39) reading. Thus, map and reality are not, and cannot be, (40) . No aspect of map use is so obvious yet so often (41) . Most map reading mistakes occur because the user forgets this (42) fact and expect a one-to-one (43) between map and reality. (44) . To understand a painting, you must have some idea of the medium which was used by the artist. You wouldn’t expect a water color to look anything like an oil painting or a charcoal drawing, even if the subject matter of all three were the same. (45) . As a map-reader, you should always be aware of the invisible hand of the mapmaker. (46) . The mapmaker translates reality into the clearest possible picture under the circumstances, and the map-reader converts this picture back into an impression of the environment. For such communication to take place, the map-reader as well as the mapmaker must know something about how maps are created.