A Series of Statistical Charts Illustrating the Condition of the Descendants of Former African Slaves - Maps show percentages of African Americans in the United States between 1800 and 1890 [LCCN2013650369]
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
Two opposing trends are shown in one mark: the crimson outline swells to carry total growth while the black fill shrinks as a proportion of it, so the reader sees the number rising and the share falling simultaneously, which no single bar chart does. Scaling the date and the fraction lettering along with the shapes turns typography into a second data channel, so the page reads correctly even before the words are parsed. The zigzag placement forces the eye through the sequence in order rather than letting it scan a row and average. Using nested silhouettes of the same country, rather than abstract squares, keeps the subject in frame at every step.
Steal this when
Steal this when a percentage falling and a total rising are both true and stakeholders keep quoting only the half that suits them. Nested same-shape marks are the right device whenever the part and the whole must be read in one glance across several time steps.