Album de Statistique Graphique - Carte Figurative de Tonnage des Marchandises Transportees par le Cabotage en 1878. (Tonnage of Goods Carried by Coastal Trade in 1878.) [12512.017]
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
One hue, three encodings - band width for flow, half-disc area for port volume, radial tick for mean distance - so the whole sheet is read with a single learned convention instead of five legends. Emptying the interior of the map removes every mark that is not data, which is why a near-monochrome plate can carry this much information without looking busy. The central circle acts as the total the parts must sum to, giving the reader a check on the whole picture, and the insets solve a real geometry problem rather than decorating: Corsica and the Mediterranean coast do not fit the frame at the scale the data needs.
Steal this when
Steal the half-disc-on-the-boundary device whenever you need per-site totals plotted on a map without the symbols colliding with each other or with the flow line. The central total circle is worth copying in any dashboard where the audience needs to know the parts add up to something they recognise.