Since circularity is a form of tolerance, it is directly related to datums.

Circularity

A geometric tolerance that limits the amount of variation from a perfect circle, often applied to cylindrical parts to ensure they rotate or fit smoothly.

Tolerance

The permissible limit or limits of variation in a physical dimension, a measured value or physical property of a material, manufactured object, system, or service.

Datums

Reference points, lines, or surfaces on an object against which measurements are made, serving as a basis for the geometric control of the part.