Foreshortening is the visual effect that occurs when an object is seen in perspective: As the angle between your eye and the object changes, the shape of the object changes as well. Although its perhaps most closely associated with figure drawings—where body parts such as arms, legs and torsos that are pointing either toward or away from the viewer—foreshortening can be present in virtually all types of subjects.
To see how foreshortening works, look at the series of drawings of the covered bridge. In the first drawing, the bridge is perpendicular to our point of view, so foreshortening isn’t necessary. However, as the bridge begins to rotate it begins to contract and becomes shorter on our visual field. Notice that as it does so, it undergoes proportional distortion and the nearest end appears to grow larger, while the other end grows smaller. The closer the object appears, the more exaggerated this effect will be. Conversely, as you move farther away, this distortion becomes less evident until it becomes indiscernible. When entirely foreshortened, as in Position 3, the near end of the bridge eclipses any exterior view of the structure’s sides.
The key to accurate foreshortening lies in drawing what you see, not what you think you see. For example, in the drawing of the woman, the foreshortened thigh is represented by a rounded-off triangular shape, not by the elongated, cylindrical form normally associated with a human thigh.