Mapped Pictures: Images as Evidence and Explanation

Overview

A representational image shows what something looks like; a mapped picture lets a viewer measure it, place it, compare it, and test the claim being made about it. Tufte's argument in Beautiful Evidence is that explanatory, journalistic, and scientific images should nearly always be mapped — fitted with scales, a coordinate grid, labels, and overlays — and that a mapping is itself a claim, so it must be held to the same standards of credibility as any explanation. The chapter's two halves are equally important: how to map an image (scale, grid, labels), and how to tell a credible mapping from a crank one (explanatory tightness, falsifiability, flatland-vs-spaceland). The current skill title drops "and Explanation"; do not — the second half is where most real failures live.

"Mapped pictures combine representational images with scales, diagrams, overlays, numbers, words, images." — Tufte, Beautiful Evidence, p. 13

Chapter and citation note. "Mapped Pictures: Images as Evidence and Explanation" runs printed pp. 12–45. Page citations throughout are printed page numbers. Four items marked (pp. 112–121) come from the adjacent "Words, Numbers, Images — Together" chapter; they are flagged where they occur because they serve this thesis more directly than any other.

Provenance across the canon. The idea does not originate here. Visual Explanations ch. 1 supplies the direct ancestor — direct labels, encodings, and self-representing scales (p. 13), the NCSA tripod-of-scales redesign (pp. 20–23), Repton's pole-people as human-scale referents (pp. 16–17). Envisioning Information pp. 108–109 gives the earliest worked case: an aerial photograph of Hoboken overlaid with a route and place labels.

§1. What a Mapped Picture Is: Image Qualities + Diagram Qualities

A mapped picture is not an illustration with decoration added. It is the fusion of two complementary things: the evidential richness of a representational image and the focusing power of a diagram. Each contributes qualities the other lacks; the map is what binds them.