Album de statistique graphique de la Ville de Paris - sheet 9 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
The plate changes its own scale and then says so on the sheet, which is the only honest way to make small values legible without misleading anyone comparing plates. Splitting each line at the fortifications turns one average into two measured halves and makes the inside-versus-outside question answerable directly from the mark. The two declining lines are given a separate hue rather than a negative width, because width cannot go below zero, and the legend inverts the tint rule for exactly those two lines and names them. The flat statement that single-tinted lines are the ones that barely moved closes the last ambiguity, so no mark on the sheet is left unexplained.
Steal this when
Use this when part of your data set is an order of magnitude smaller than the rest and deserves its own plate rather than a squashed corner of the main one. The exception handling is the thing to copy: give declines their own colour, invert the rule for them in the legend, and say plainly what a flat mark means.