Fig. A-4. From the photomosaic obtained by Mariner, the U.S. Geological Survey is preparing an Atlas of Mercury. A control net of Mercury has been established together with coordinates of over 1000 points from the Mariner 10 photographs. The series of maps of Mercury will be produced at a scale of 1:5,000,000. Topographic and albedo features are portrayed by airbrush techniques similar to an earlier series of maps of the Moon and Mars. The map reproduced here shows the coverage obtained during Mercury I to a scale of 1:25,000,000. The diagonal gap across the map was, of course, filled in by the photographs obtained later at the second encounter.