A labeled topographic map of the Moon's near side (the side always facing the Earth) (source: USGS). North is at the top and South at the bottom. Using a selenocentric coordinate system (a system based on the view from the Moon), West is on the left and East on the right. Using a geocentric coordinate system (a system based on the view from the Earth) the western side of the Moon is on the right and the eastern side is on the left. Older maps tend to use the geocentric system, but space-age maps tend to use the selenocentric system.
     Since the Moon has no air or water and hence no "sea level", zero altitude is set at the Moon's mean (average) radius of just over a thousand miles. Altitudes below that use bluer tones suggestive of oceanic regions on the Earth, and altitudes above that green and redder tones suggestive of land regions on the Earth (areas shown in gray have no reliable altitude data). As the result the lunar maria, once thought to be oceans, are shown as though they really were oceans, while the lunar terrae, once thought to be highlands, are shown as though they really were continents.