linear perspective

n. A cue used to perceive depth in which the size of an image on the retina is used to judge its distance. So the same thing seen close up casts a large image on our retina and a smaller one when far away, and we use the difference in size to estimate depth or distance. An instance of this most have experienced occurs when railroad tracks run away from us and the near tracks look larger than the far tracks and we perceive depth instead of that the track shrinks as it goes away from us.