Closure is the name for the way in which humans perceive a set of individual unconnected elements as part of a single recognisable object or pattern rather than individual pieces. This is one of a number of principles relating to Gestalt psychology, and is so strong that people close gaps and fill in missing information to complete a pattern if necessary.
When individual elements are positioned along a circular path. they are perceived as a circle before they are seen as individual elements. This ‘way of seeing’ is automatic and unconscious, representing a preference for simplicity of form and the desire for pattern over random information (as seen in the Law of Pragnanz).
Humans also ignore gaps and ‘fill in’ contour lines. In the above image there are no circles or triangles, but your mind will fill in the ‘missing’ information to create familiar shapes and recognisable patterns. So the law of closure is strongest where pieces of information are similar to simple and recognisable shapes and patterns, as in basic geometric forms, and also when they are close to each other (The Law of Proximity). For designers, this means that closure can be encourages through the use of transitional elements where simple patterns are not easily perceived, using subtle cues to direct perceptions to certain aspects of the design. Where the effort required to see individual elements is greater than the effort required to see a ‘whole’ picture, then the whole picture will be preferred.
Closure means that designers can reduce complexity by reducing the number of elements in a design used to communicate information. Logos composed of recognisable elements do not need to be complete and can use incomplete elements to communicate the required information. Reducing the number of lines, reduces the complexity of a design and makes it more interesting to look at, as the viewer will subconsciously want to ‘complete’ the design, making them more curious to understand the design. Closure is a principle that is common in storytelling, most especially in comic books (with a set of discrete scenes across time). Of course, cinema works this way too, although we are never aware of the individual elements.
The great thing about using closure in design and storytelling is that the viewer is an active participant in interpreting information (they contribute to the information as well as the designer or storyteller).
In summary, closure is a great way to simplify and increase interest and involvement in a design, by invoking simple patterns that are recognised and removing or minimising elements that can be completed by the user. Where there are more complex patterns, transitional elements can help provide cues to find the full form or pattern.
Universal Principles of Design by Lidwell, Holden & Butler
Understanding Comics: The Invisible Art by Scott McCloud