Answer:
As discussed in the last chapter, all artists deal first with empty space. Large, open spaces that seem endless are beautiful in nature, but most humans do not choose to make their homes in the midst of them. We like to limit an area and then populate it with buildings. For the two-dimensional artist, the first important design decision is also how to limit space and define its borders. The boundaries demarcate what is known as the picture plane, the playing field of the art elements. Its frame establishes a separate arena for artistic activity from the whole world that surrounds it. Its proportions will determine the effect of whatever is within its borders.
Explanation:
Answer is The borders of the artwork. Above is from the text book