Visual Encoding

Visual encoding is the choice of which visual channel — position, length, angle, area, color, shape — you use to represent a number. Every chart is really a mapping: a bar chart encodes value as length, a scatter plot encodes two values as horizontal and vertical position, a heatmap encodes value as color intensity.

The choice matters because the human eye reads some channels far more accurately than others. Decades of experiments rank position along a common scale as the most precise, then length, then angle and area, with color saturation among the least precise. The practical lesson: put your most important comparison on the channel people read best — usually position or length — and reserve color for grouping rather than for exact quantities.