The Georgia Negro: A Social Study - Circle graph shows percentage of African Americans and whites in various occupations [LCCN2005676812]
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
Splitting one pie into two half-fans that share a single vertex is what makes the comparison work - because both populations radiate from the same origin point, wedge angles can be read against each other directly instead of the reader hopping between two separate circles. Mirroring rather than stacking the fans means the crimson agricultural blocks land almost identically opposite each other, which neutralises the obvious similarity and throws all the attention onto the wedges that differ. Colour carries the category and the legend sits out in the margins, so the figure itself stays uninterrupted by text.
Steal this when
Use it when two groups share the same category set and the story is the difference in the small categories, not the big one they have in common. The shared-vertex mirror is the move whenever side-by-side pies would force the reader to compare angles across a gap.