Carte figurative et approximative du mouvement des voyageurs sur les principaux chemins de fer de l'Europe en 1862
The pattern
This still is filed under Data as proof.
Define
A chart, map, or count that is the argument, not an illustration next to the argument.
Mechanism
Sighted evidence. The reader is asked to believe their eyes: a bar, a share, a spread on a map.
Verdict
The claim is comparative or quantitative and the figure can be read without a caption doing the sell.
Why it works
The band width is passengers per kilometre of line, not raw passengers, so the design decision that matters happens before anything is drawn: the normalisation is what makes a short busy railway comparable to a long thin one. Britain is lifted into an inset rather than shrinking the whole map to accommodate it, which protects the main scale instead of flattening every difference to fit the outlier. The Explication names precisely where numbers were inferred rather than measured, and the two tables put the underlying figures on the same sheet as the picture, so the graphic and its evidence cannot be separated.
Steal this when
When comparing channels, regions or accounts of wildly different sizes, normalise per unit before you plot anything, and lift the outlier into an inset rather than rescaling everything around it.