Carte figurative et approximative representant pour l'annee 1858 les emigrants du globe
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 quantity is encoded as the thickness of the thing itself rather than as a bar standing next to it, so scale is read at the same instant as route and direction and no eye movement to an axis is needed. Colour carries origin and width carries volume, two independent channels on one mark, which is why seven flows can overlap without collapsing into noise. Stripping the basemap back to blank coastline is the load-bearing decision: it turns geography into background and the flows into figure.
Steal this when
Use this structure when the question is where something goes and how much of it, and the audience already knows the territory - budget across business units, traffic across channels, headcount across offices. It is the right form whenever a table of origin-destination pairs is technically complete but nobody can see the shape of it.