The picture-space should be filled, but need not be crowded, and it must be remembered that in judging balance, not only the masses of the subject, b… - Arthur Hammond

The would-be picture-maker must learn to think pictorially; he must try to regard a picture as a pattern, as an arrangement of lines and shapes, making in themselves a pleasing and satisfying design, quite apart from the objects represented. The lines will form certain shapes, and the shapes will vary in tone; some may be light, some dark and some of intermediate shades of gray, which we call halftones.

A photograph can be made with an uncorrected lens, or with no lens at all by making an exposure through a fine needle-hole in a thin metal disc, and the result may be a picture showing the characteristic virtue of photography, the rendering of infinitely delicate gradations of tone. This is where photography stands alone, and this is the distinguishing quality which has given it a place among the fine arts.

...but the fundamental element of picture-making is the cutting of the picture-space by lines or edges of tones, and this is what is known as "spacing".