Album de statistique graphique de la Ville de Paris - sheet 12 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
Panel A and panel B are the same phenomenon measured two ways, count then rate, placed adjacent so the reader performs the correction himself instead of being told the conclusion. The legends do the work that footnotes do in a report: they name what is excluded, which population base was used for which decade, and where the numbers came from, which is what lets a hostile reader accept the chart. In panel C the light tint is the current year and the dark the multi-year mean, and the cap band at the top of each column is coded to show whether the excess belongs to the year or to the baseline, a single mark that answers direction and magnitude at once. Setting three panels of different subjects in the same ruled frame, each self-contained with its own key and legend, is the album's core layout move and the direct ancestor of the modern dashboard card.
Steal this when
Use this when a long-run count is going to be read as a trend but the denominator has also been growing, and the honest answer needs both. Put the count and the rate side by side, and write a legend under each that names the exclusions, the base and the source so the chart survives scrutiny.