The principle of unity is perhaps the most important of the design principles, yet it is often the most difficult to understand. Unity is the fundamental principle of design and it is supported by all the other principles. If a design is not unified, it cannot be considered successful.
Unity creates an integrated image in which all the elements are working together to support the design as a whole. A unified design is greater than the sum of its parts; the design is seen as a whole first, before the individual elements are noticed . Unity can be compared to harmony, integrity or wholeness.
Unity is based on the gestalt theory of visual perception, which states that the eye of the viewer seeks a gestalt or unified whole. This means that the viewer is actually looking for a connection between the elements, for some sort of organization, for unity in the design.
A gestalt is created because the mind simplifies and organizes information. It does this by grouping elements together to create new wholes. Understanding how the mind groups elements (by proximity, similarity, continuation and alignment) helps us understand how unity can be achieved.
Proximity is based on grouping by closeness; the closer elements are to each other, the more likely we will see them as a group. Proximity is one of the easiest ways to achieve unity.
Repetition is based on grouping by similarity; elements that are similar visually are perceived to be related. Any element can be repeated – line, shape, color, value or texture – as well other things such as direction, angle or size. Repetition helps unify a design by creating similar elements and is one of the most effective ways to unify a design.
Alignment consists of arranging elements so that their edges are lined up. The common alignment allows the eye to group those elements together. A grid is often used to create unity through alignment, not just in a single design but also between related designs (the pages of a magazine or book, for example).
Continuation means that something (a line, an edge, a curve, a direction) continues from one element to another. The viewer’s eye will follow the continuing line or edge smoothly from one element to other and the mind will group the elements because of this connection. Implied lines are one example of continuation.