Data visualization is a specialized skill, but its principles — clarity, signal-to-noise ratio, appropriate encoding — apply to all visual design. Understanding them makes you a better designer even if you never design a chart.
The Signal-to-Noise Principle
Edward Tufte's data-ink ratio: maximize the ink (or pixels) dedicated to actual data, minimize the ink dedicated to everything else. Applied to UI: maximize the pixels that communicate the thing users came to see, minimize the pixels spent on chrome, decoration, and navigation overhead. This principle produces both better charts and better interfaces.
Encoding Channels
Data is encoded through visual channels: position, length, angle, area, color hue, color saturation, shape. These channels have different accuracy and appropriate use cases. Position (the y-axis of a bar chart) is the most accurately perceived. Angle (pie charts) is poorly perceived. Color hue doesn't encode quantity well; color saturation can encode one dimension of magnitude.
Applied to UI design: use the most accurate encoding channel for the most important information. Don't encode critical status through color alone — color is poorly perceived under screen brightness variations and inaccessible to colorblind users.
Dashboard Design
Dashboards fail in predictable ways: they show data rather than insight, they have too many equally prominent metrics, and they don't answer the question "so what?" The best dashboards have one primary metric that dominates the view, supporting metrics that explain or contextualize it, and explicit anomaly highlighting that tells users when to pay attention.