What characteristic of a person's face primarily determines its shape?

The shape of a person's face is primarily influenced by the structure of the jawline. The jawline defines the lower contour of the face and contributes significantly to its overall shape, such as whether it appears more oval, square, round, or heart-shaped. A pronounced or softer jawline can dramatically alter the perception of a person's face shape.

While other features like the forehead, cheeks, and nose do play a role in facial aesthetics, they tend to complement the overall appearance rather than primarily determine the outline. The jawline is particularly distinctive because it frames the face and contributes to its angularity or roundness, making it a central factor in assessing facial shape.