Introduction to Visualization

Visualization is the communication of information using graphical representations. A picture is worth a thousand words because a picture can be processed in parallel by the brain whereas words have to be processed sequentially. Moreover, pictures can be understood in a language independent way.

There are various ways that data can be presented to the user.

Importance of Visualization

The importance of visualization cannot be overstated. Simply put the key areas that visualization is important are:

Brief History of Visualization

Pictures have been used to communicate since prehistoric times. Some of the oldest writing systems used pictures to encode symbols and words - logograms. Limestone tablets found in Mesopotamia are pictographic and the beginning of syllabic and cuneiform scripts.

From the Egyptians we get hieroglyphics - pictorial writing. These writings were born out of necessity - travel, commerce, religion, and communication.

John Snow's map of cholera deaths in London in 1854. Each stacked bar represents one deceased individual. He found that cholera occurred entirely among those who drank from the Broad Street water pump. He had the handle of that pump removed ending the epidemic that had taken more than 500 lives.

Minard produced a brilliant representation of linked geographic and time series data. The map emphasizes the loss of troops during the Napoleonic Russian expedition. The size of the French army went from 400,000 to 10,000.

A break through came in data visualization with the abstract representation for axes. Examples include:

Vizualization Today

We use visualization to communicate both qualitative and quantitative information. Modern visualizations use digital media. They provide a rich description of the data. Consider the Anscombe Quartet. They have the same mean and standard deviation but are very different distributions.

Visualization was once considered to be a sub-field of Computer Graphics. It uses graphical primitives like points, lines, areas, and volumes. But visualization goes beyond graphics. It is connected with data, most often there is statistical processing and there is a narrative involved.

Milestones in Data Visualization

Process of Visualization

This is a simplified overview of the process:
  1. Data - what type is it?
  2. What do you want to do with it?
  3. How do you want to display the visualization - static or interactive?
Visualization is part of a larger process - exploratory data analysis, knowledge discovery, or visual analytics. The visualization pipeline is as follows:

Human Perception and Visualization

If the goal of the visualization is to accurately convey information with pictures then human perceptual abilities have to be considered. Consider the following illusions.

Most people cannot gauge textures accurately but our abilities to perform relative comparisons are much stronger than absolute ones. About half the human brain deals with visual input and the processing is parallel and continuous. The preattentive processing is fast and can identify differences in color or texture. Other features the system deals with are line orientation, length, width, size of an object, curvature, grouping, and motion.

The Gestalt School of Psychology attempted to define a set of laws by which we define patterns. These laws included rules about proximity, similarity, continuity, closure, symmetry, foreground and background, and size.