THE MARS GLOBAL SURVEYOR laser altimeter, with its 30-cm precision, is rendering the best topographic maps yet for the red planet. Two highlights from a series of articles in the 15 December issue of Geophysical Research Letters---Mars is less flattened than was thought: its mean equatorial and polar radii are measured to be 3396 and 3373 km; and a possible shoreline of a presumed ancient polar ocean was studied.