This dark "sea" is diagonally opposite the Mare Crisium on the lunar disc, near the south western limb.

Unlike Crisium, it is not discrete from the other Maria, and is a little smaller at around 250 miles north-south and 275 miles east-west, correcting for foreshortening. However, at times when Crisium is not visible it makes a useful ready reckoner for judging the distances between lunar features.