The Georgia Negro: A Social Study - Circular bar graph shows value of furniture between 1875 and 1899 [LCCN2013650445]
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 spiral is a bar chart that ran out of paper. Encoding value as arc length on a coil lets a range of roughly seventy to one fit on a single sheet at a constant unit, with no logarithmic axis and no broken scale, so the tiny 1875 stub stays visible at the same measure as the 1899 band. The cost is real and worth knowing before you copy it - once bars are curled, the reader compares by how far round each ribbon travels rather than against a shared baseline, so precision is traded for the felt sense of accumulation, and the printed key in the corner is what repairs the loss.
Steal this when
Use it when a series spans orders of magnitude, you refuse a log scale, and the impression of accumulation matters more than exact comparison. Always pair it with a plain numeric key, as this plate does, or the shape becomes decoration.
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