Data visualizations are designed to help people discover and understand connections between the elements they depict. They accomplish this by capitalizing on the largely unconscious information processing capabilities of human visual perception systems. These capabilities were intuitively clear well before we were able to explain them scientifically. William Playfair, an early visualization innovator, anticipated the study of modern human visual cognition when he wrote that one of the goals of charts and graphs was to convey information ‘without the fatigue and trouble of studying the particulars of which [they are] composed’. Modern science has confirmed Playfair’s claim. The field of human perception has demonstrated that we process visual information more quickly and in far greater density than information from the other senses. We perceive visual cues and recognize patterns without conscious access to the underlying processes. This information processing occurs in the background, reducing cognitive load and leaving more time and energy for higher-level processing, analysis, and evaluation.