Learned cues are used by artists to portray depth on a two dimensional canvas.
Learned Cues: Even if a person does not have binocular vision, distance can be perceived on the bases of learned cues.
For example, we have learned that parallel lines, which never meet in geometry class, do come together in the distance. Just look down the railroad tracks (after the Amtrak has passed).
This is a cue for distance which artists use to portray depth on a flat canvas.
Degrees of shading, and the height of objects on our visual field are other distance cues.
One cue that we don't often think of is called parallax. As you drive along a road, objects (like telephone poles) that are close to you move in the opposite direction faster than those that you might view in the distance. And of course, the moon never seems to move at all.