In the past, data size and variety did not impose much of a challenge; therefore, perceiving and analyzing data was straightforward. Today there are large quantities of data in innumerable fields, and visualization can provide valuable assistance to humans for perceiving and interacting with visualization of the data. Human factors contribute significantly to the whole visualization process in order to better understand data and aid in decision-making tasks.
Visualization techniques can be categorized into two areas:
Most visualization systems are designed so that humans and computers can cooperate, each performing the following tasks:
- Visually representing data to enhance data analysis
- Visually displaying models, interpretations of data, ideas, hypotheses, and insight
- Helping users to improve their models by finding either supporting or contradictory evidence for their hypotheses
- Helping users to organize and share their ideas
New insights into visual perception are arising from work in various disciplines besides information visualization, such as human factors and human-computer interaction. One of the great strengths of data visualization is our ability to process visual information much more rapidly than verbal information. Psychologists studied perceptual organization during the 1920s in Germany, and the first group of them was the Gestalt Theorists.
The word Gestalt means "organized whole" or, in other words, when parts identified individually have different characteristics to the whole. For example, for describing a tree, you can say that it has different parts such as the trunk, leaves, branches, fruit (in some cases). However, when we look at an entire tree, we are not conscious of the parts, but aware of the whole object—in this case, the tree.
The principles of Gestalt perception are as follows:
- Proximity: Objects that are close together or connected to each other are perceived as a group, reducing the need to process smaller objects separately.
- Similarity: Objects that share similar attributes, color, or shape are perceived as a group.
- Common fate: When both the principles of proximity and similarity are in place, a movement takes place. Then they appear to change grouping.
- Good continuation: Some things are important as a whole, which means if there are interruptions, then it changes the perceptive reading. In the following image, we perceive the two crossed lines instead of four lines meeting at the center:
- Closure: Even if a part of the border of a shape is missing, we still tend to see the shape as completely enclosed by the border and ignore the gaps.
It is very useful to know these principles for creating any visualization method.
Let's elaborate this further with an example. Proximity refers to the visual approach of grouping shapes together if they appear similar to each other. Such a group is usually perceived as a single unit. For instance, the following image shows how one can distinguish proximity:
