Perspective is

Concept: Perspective, in drawing and visual art, is the technique used to represent three-dimensional depth and spatial relationships among objects on a flat, two-dimensional surface — it creates the illusion that some parts of a drawing are nearer to the viewer and others farther away.

Application: Among the four descriptions offered, only "the depth of the surface" names this quality — the near-far spatial depth that perspective represents on a drawing's flat surface; the other three describe fixed measurements of a figure's own shape, not this illusion of space in the scene.

Cross-check — the other three descriptions, by their own value:

• the height of figure — a linear top-to-bottom measurement of the figure itself.

• the length of figure — a linear side-to-side measurement of the figure itself.

• the roundness of the figure — the curvature of the figure's outline, a property of its shape.

Result: Perspective is, therefore, the depth of the surface.