[1] It is located to the south-southeast of the larger crater Catharina, in the area framed by the Rupes Altai scarp.

Some distance to the northeast is the Mare Nectaris, with the flooded craters Beaumont and Fracastorius.

The crater rim of Polybius appears slightly distended in the northeast, and has a cut through the northern wall.

The interior floor is flat and almost featureless, with no central rise.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Polybius.