Final answer:
In design, establishing equal or appropriate proportions to create symmetry is known as balance. Balance can be symmetrical, as in bilateral symmetry where elements mirror each other, or asymmetrical, where elements are different but visually weigh the same in the arrangement.
Step-by-step explanation:
Establishing equal or appropriate proportions to create symmetry in a design is called balance. Balance in art refers to the distribution of visual weight within a composition. Symmetrical balance is where elements of the artwork are mirrored on either side of a central axis, giving it a sense of stability and formality. This type of balance can be seen in works such as Perugino's painting, 'Christ Giving the Keys of the Kingdom to St. Peter.' On the other hand, asymmetrical balance involves a composition where elements are not mirrored but still achieve a visually balanced look through a harmonious arrangement of different elements, creating a more dynamic feeling. An example of asymmetrical balance is the Classical Greek sculpture Doryphoros (The Spearbearer) by Polykleitos.