When there is any illusion of depth in the picture, the picture plane is similar to a plate of glass behind which pictorial elements are arranged in depth.
Pictures have geographical bearings.
We can describe where we want to look within the space of an image.
Left or right? Top or bottom?
We also feel, when we view a picture, that some areas of the image are closer to us, and some areas are farther away. A picture creates a three-dimensional pictorial space with perceptible depth.
Artists indicate the supposed distance of subjects beyond the picture plane through the use of changes in the sizes of things, the ways they overlap each other, and (when subjects are placed on the depicted ground, as opposed to flying above it) by positioning them on the area taken up by the depicted floor, ground, or a body of water.
Abstract Expressionists worked directly on the plane itself, unconcerned with recession in depth.
The most basic elements of composition result from deep psychophysical reaction to placements on a flat plane.
The most obvious physical attribute of the picture plane is the felt axis, a straight vertical at a right angle to the earth. We feel this axis through our sense of balance, and any deviation from absolute verticality can be detected easily - it often has a disconcerting effect, as in the leaning tower of Pisa. It is through the vertical axis that we identify up and down in our field of vision and our picture.
When the picture plane of a painting is generally the way we see it in nature, we call it realistic or in-depth. Correct perspective is employed to accomplish this, through the Elements of Line and Shape. In the in-depth picture plane, the foreground is at the bottom and is seen as close at hand. The middle-ground includes the horizon and is in the middle of the picture. The background goes to infinity and is shown at the top of the picture:
