The Georgia Negro: A Social Study - Diagram shows two maps of Georgia, one from 1870 and the other from 1880, with colors to mark the number of African Americans in each county [LCCN2013650425]
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
Small multiples with a shared scale: the same outline, the same key, only the year changes, so every difference the eye catches is real signal. Splitting the key into two corner blocks turns a housekeeping element into the compositional counterweight that holds the diagonal, which is why the sheet feels composed rather than laid out. Circular key swatches rather than squares read as points on a map rather than as boxes of ink, softly tying legend to territory.
Steal this when
Use this when a before-and-after on the same geography or the same segment set is the whole story. Hold every variable but time constant, and place the two frames on a diagonal so the reader's eye crosses the sheet instead of stopping at the first panel.