A control net of Mercury has been established photogrammetrically by using the Mariner 10 pictures; coordinates of 1328 points are given. The Mariner 10 coordinate system uses a system of longitudes in which the twentieth meridian passes through the center of the small crater Hun Kal and the spin axis is assumed normal to the orbital plane. A reference mosaic of Mercury has been published, and a series of 1:5,000,000 maps is now being produced.