To the southeast is the walled plain De La Rue.

Thales has a sharp, circular rim that has received little erosion.

The sides have a higher albedo than the typical lunar terrain.

In 1892, E. E. Barnard observed a pale haze fill the crater interior, while the surroundings remained clear and sharply visible.

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