13.3 Use perceptually accurate encodings

Position along a common scale and length are generally easier to compare accurately than angle, area, volume, or colour intensity. This is why bars and dot plots often communicate category differences more clearly than pie charts or bubbles.

Bar charts should normally begin at zero because bar length encodes magnitude. Line charts can use a narrower vertical range when the scale is clearly shown and the purpose is to examine change. The decision should preserve honest perception rather than follow a rule mechanically.