Wallace is the remains of a lunar impact crater that has been flooded by lava.
[1] It lies in the southeastern part of Mare Imbrium, northeast of the crater Eratosthenes.
The crater rim forms a somewhat polygonal outline, and is broken in the southeast.
The floor is flat and devoid of significant features, but it is overlain by ray material from Copernicus to the southwest.
By convention, these features are identified on lunar maps by placing the letter on the side of the crater midpoint closest to Wallace.