Album de Statistique Graphique - I. Circulation des Routes Nationales de la France par Section de Comptage D'Apres les Recensemens de 1894. (Circulation on the trunk roads of France by section counted.) [12525.032]
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 small-multiple gutter of city insets is the real engineering: the national map answers where traffic is, and the identical repeated insets answer how it behaves where it is worst, without ever changing the encoding, so the eye can hop between scales without relearning anything. Holding the sea as a flat unsaturated green and leaving land white gives the red a monopoly on saturation, which is why the arterial wedges pop out of a network that is otherwise near-uniform. Using one hue at varying width rather than a colour scale avoids the binning that would have hidden the continuous distribution of traffic.
Steal this when
Use it when you have a dense uniform network and the story is concentration - every site, road or link looks equal on paper but a few carry everything. Keep one hue, vary width, and run a fixed strip of same-scale insets for the congested nodes rather than trying to zoom the master map.