6 ideas
The data-ink ratio is the proportion of a graphic's ink devoted to displaying actual data versus decoration or redundancy. Maximizing this ratio — by erasing non-data ink and redundant data ink — strips a graphic down to the marks that carry information, increasing clarity per unit of visual attention.
Decorative elements like moiré patterns, heavy grids, and ornamental graphics ('chartjunk') add visual noise without adding information, often distorting or obscuring the data. Such embellishment insults the viewer's intelligence and signals that the data itself is too weak to stand alone.
The lie factor is the ratio of the size of an effect shown in a graphic to the size of the effect in the underlying data; a value of 1.0 means the representation is accurate. When this ratio exceeds 1.05 or falls below 0.95, the graphic distorts reality, frequently because the visual area grows as the square or cube of a one-dimensional quantity.
Excellent graphics give the viewer the greatest number of ideas in the shortest time with the least ink in the smallest space, and they reward attention to large data sets rather than oversimplifying. The goal is high data density and multivariate complexity made coherent, not stripped-down summaries that hide structure.
Charles Minard's 1869 flow map depicts Napoleon's 1812 army marching into and retreating from Russia, encoding six variables at once: troop size, location in two dimensions, direction of movement, temperature, and time. The dwindling band width vividly shows the catastrophic loss of men, demonstrating how a single graphic can narrate complex history.
Small multiples are series of the same graphic repeated at the same scale, each showing a different slice of data such as a different time period or condition. Because the design stays constant, the eye can compare across panels effortlessly, making patterns of difference and change immediately visible.