Statistical Atlas of the United States, Based Upon the Results of the Eleventh Census (1890) - plate 9: Center of population at each Census: 1790 - 1890
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
Reducing a hundred years of migration to one index point makes an abstraction trackable, and plotting it eleven times turns a statistic into a trajectory the eye completes on its own. Naming familiar cities along the path gives the reader anchors to convert an abstract drift into a felt distance. The second map is a deliberate change of scale: after the sweeping continental claim it zooms to a named crossroads in Indiana, which makes the abstraction feel verifiable rather than rhetorical. Setting both maps in one ink on a text page, inside the book's own border and running head, quietly signals that this is argument in the body copy, not a display plate.
Steal this when
Use this when a long trend has to be made physical, and you can define one honest index point that moves, then chart its path instead of the underlying series. Follow the wide view immediately with a zoomed view of the current position so the abstraction lands somewhere the reader can picture.