Album de Statistique Graphique - Tonnage de chemins de fer Francais en 1896. Grave et Imprime par A. Simon, Paris [13188.016]
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 plate lets the encoding saturate on purpose. Where earlier sheets keep every band separable, here the coalescing of the north into a solid field is itself the message about industrial concentration, and the designer buys back the lost detail with four scale-break insets rather than by rescaling and flattening the whole country. Using a single hot ink against untouched paper means the read is pre-attentive - the reader sees the shape of French heavy industry before reading a single word. The footnoted observations column is what keeps a graphic this aggressive defensible line by line.
Steal this when
Use it when concentration is the finding and you would otherwise be tempted to log-scale or cap the values to keep the chart tidy. Let the dense region go solid, say so, and recover the detail with insets instead of compressing the scale.