The Gestalt school of thought was studied in the early last century to evaluate how brain perceives the world around us. It is how we ought to organize our visualizations to be effective at conveying information.
The principle of proximity states that when elements are placed close to each other, human brain perceives it as group and that they are related. This principle is so powerful that it rescinds the factors such as shapes, colours that differentiates the elements.
The principle of similarity states that the human brain naturally groups similar looking elements and perceive it to have same functionality. For example, the elements with same shape, colour etc. irrespective of how they are arranged.
This principle is very much similar to proximity. It uses colour or boundaries to highlight or contrast information. This is another way by which human brain perceives groups i.e. when a set of elements are inside a closed region they are a group. This principle again overrides the shape colour and other factors.
The principle of closure states that the human brain perceives the visual elements between the gaps and tends to arrange it into a single recognisable pattern.
The principle of continuity states that the elements that are arranged in a curve or a line are perceived to be related to each other. This principle again overrides the colour of elements.
The principle of connection or connectedness states that human brain has the ability to perceive that elements connected together by a line are related to each other than the elements that stay unconnected irrespective of their shape colour etc.,