Album de statistique graphique de la Ville de Paris - sheet 7 of 12 (BnF btv1b52505495j)
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
Width on a line is a quantity channel the eye judges well, and pinning it to the real route means the reader gets magnitude and geography in the same mark. Splitting each band into a light half and a dark half packs direction, inbound against outbound, into a band that would otherwise carry only a total. The inset at a declared quarter scale gives the whole-city figure without letting the summary swamp the corridors, the same range trick used on the octroi plates. The nota and the parenthetical exclusion of transit are printed on the sheet, which stops the reader importing a definition the chart does not support.
Steal this when
Use this when volume moves along a known network, such as shipping lanes, pipelines, referral paths or a supply chain, and the route matters as much as the amount. Encode the amount as band width, split the band to carry direction, and put the total in a small inset at a scale you state.