# Tufte Mapped Pictures

> Use when preparing or auditing an image meant to serve as evidence — a photograph, scientific micrograph, satellite or astronomical picture, diagram, drawing, or painting — and it needs measurement scales, a coordinate grid, or labels; also when judging whether a mapping or overlay laid on top of an image is a credible explanation or an unfalsifiable one.

- Skill: `jpoindexter/tufte-mapped-pictures` (Agent Skill)
- Install (CLI): `npx skillmds@latest add jpoindexter/tufte-mapped-pictures`
- Raw SKILL.md: https://api.skillmd.com/api/skills/jpoindexter/tufte-mapped-pictures/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: jpoindexter (https://skillmd.com/u/jpoindexter)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/jpoindexter/tufte-mapped-pictures

---

# 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.

| Image contributes | Diagram contributes |
|---|---|
| Representational — shows the real thing | Contextualizing — places it on a shared scale |
| Local, specific — this individual case | Abstracting — pulls out the general structure |
| Realistic, unique, detailed | Focusing, explanatory — directs attention, makes a claim |

The test for whether a picture has been *mapped* (not merely captioned): could a stranger, with no prior knowledge, extract a measured value and locate any feature in shared coordinates without leaving the image? If the scale, grid, or labels live only in a separate caption or legend that travels separately, the image is still unmapped.

**DO:** Decide the single number or comparison the viewer should be able to read *off the image*, then build the scale/grid/labels to deliver it.

**DON'T:** Treat annotation as a finishing coat applied after the image is "done" — added late, it decorates instead of measures.

---

## §2. The Scale of Measurement: Put Every Image on the Universal Ruler

The first and most-skipped obligation. Without a scale of measurement, sizes and distances are guesses, and two images cannot be compared at all. Tufte's worked examples are a catalog of how to attach a ruler to an image.

### Forms of scale reference (worked from the chapter)

- **Native unit overlaid on the drawing.** Galileo recorded Jupiter's satellites with hundreds of annotated, scaled sketches — observation time noted, the satellites labeled, distances measured in *Jovian-radii*, the only relevant unit available. The annotation is what turned telescopic sketches into credible quantitative evidence of orbital motion.
- **An explicit scale bar with a stated conversion.** The Crick–Watson DNA demonstration model is photographed with a scale reading 0 to 10 ångströms. The payoff is the conversion the scale forces into view: 1 cm = 100,000,000 ångströms (10⁸), 1 inch = 254,000,000 ångströms. The bar both quantifies the model and signals the image is explanatory, not commercial art.
- **A comparison object of known size.** Placing Earth beside Saturn gives millions of casual viewers a sense of scale that a lone "celebratory photograph" never does. Scale is part of the news whatever the marketing department believes.
- **A ruler drawn into the plate.** Brisson/Martinet's 1760 cockatoo carries a "scale of 6 inches" (échelle de 6 pouces) at lower right; objects of roughly known size (plant leaves) reinforce it.
- **Rescaling instructions when the drawing is reduced (pp. 34–35).** Lilienthal's plate calculates the wing area of a 4 kg stork with rectangles and measurements overlaid on the drawing. Lilienthal drew it at **⅛ natural size**; because *Beautiful Evidence* reproduces it at a further reduction, Tufte adds the instruction to **multiply by 9.4 to obtain real stork size**. The two figures are not in conflict — ⅛ is the original plate's scale, 9.4 is the factor for the reproduction in front of you, which is exactly why a rescaled image must state its *own* factor rather than inheriting the original's. The flapping-wing space-time tracings carry their own separate scales (1/20 head-on, 1/50 bird-side view). Tufte's complementary complaint on the same page: this plate and 7 others were **folded up and stuffed in the back of the book**, convenient for printing and binding and inconvenient for seeing and reading.

### The anti-example: the "different and unknown scale"

Bloch's *Ichthyologie* (1795) draws 216 fishes — seahorses to sharks — each forced to fill an *identical* framing box. The beauty hides a defect: every fish therefore has a *different and unknown* scale, so no two can be compared. Tufte's fix is the redraw — gentle redesigns that add 0/5/10 cm measurement scales and mark cross-section locations, "mapping the images on the universal ruler."

### Density is not a substitute for scale, but it is the reward

Dense annotated images repay the scale apparatus. Dürer's 1525 construction packs ~48 numbers mapping 3 line-traces (one of 100 such plates in a book literally titled *a course in the art of measurement*); Mersenne's 1636 lute engraving carries 80 numbers (312 digits) over a 19-string lute and 21-string theorbo. The lesson: when the image is information-rich, the ruler is what makes that information legible rather than ornamental.

| Image context | Minimum scale obligation | Common failure |
|---|---|---|
| Scientific micrograph / AFM | Bar with unit (nm, µm) *in* each panel; state z-range | Beauty shot, no scale (the celebratory image) |
| Astronomical / deep-space image | Scale + comparison object; native unit | "Notoriously unscaled and dequantified" PR image |
| Natural-history / specimen plate | Real ruler in the plate, not identical framing boxes | Bloch's "different and unknown scale" |
| Reduced/reproduced drawing | Scale bar + explicit rescale factor | "Not to scale" — a confession, not a fix |
| Engineering / forensic drawing | Scale of feet/metres + dated conditions | Dimensions buried in caption |

**DO:** State the conversion (1 cm = N units) so the viewer can compute any measurement directly.

**DON'T:** Force heterogeneous subjects into identical frames — it silently rescales each one and destroys comparison.

---

## §3. The Map Metaphor: Labels Belong on Images, Grids Scale Them, Context Makes Data Credible

Bayer's *Uranometria* (1603, engravings by Alexander Mair; pp. 20–21) is Tufte's cleanest statement of the map metaphor. The star atlas locates stars on a measured, labeled two-dimensional grid, encodes brightness by star-size (like city-size on a road map) and by Greek letter (α brightest, β next), and so yields a *dual context*: the universal sky grid plus the local neighborhood of nearby stars.

> "For showing evidence, the map metaphor suggests that labels belong on images, that external grids help to scale images, and that data are more credible when contextualized." — Tufte, *Beautiful Evidence*, pp. 20–21

Three operational rules fall out of the metaphor:

1. **Labels go on the image**, next to what they name (see §5).
2. **An external grid scales the image** without competing with it (keep grid weight well below the data marks).
3. **Context confers credibility** — an isolated mark is a rumor; the same mark on a shared grid is evidence.

Note Bayer's honest weakness, which Tufte flags rather than hides: where real stars run out, the *myth* (Leo the lion) fills the gap — a reminder that the decorative layer must never be confused with the measured one. Galileo's telescope soon replaced the myth with real stars.

---

## §4. The Universal Grid: x, y, z, t

The chapter's governing principle, stated at the close:

**Every image — whether for explanation or for exploration — should reside on the universal measurement grid of 3-space and time: x, y, z, t** (chapter close, p. 45). The grid must travel with the image through every transformation: it should accompany rescaling and zooming in and out, so a viewer never loses the absolute frame while inspecting a detail (as in the 3-image photosynthesis sequence, where every magnification still carries its scale bar and z-range).

Relative-only scaling is insufficient. Peterson's bird field guide scales birds *relative to one another*, which is not universal — Tufte's remedy is to add a constant external referent (a common plant, a few clams for shorebirds) or, far better, a real measurement scale. The principle generalizes the special cases of §2 and §3: a scale bar fixes one axis, a grid fixes two, the universal grid fixes all four and binds every image in a document into one comparable space.

**DO:** Keep the universal grid (or at minimum a scale + orientation) attached through every zoom, crop, and rescale.

**DON'T:** Rely on within-image relative scaling ("this bird is bigger than that bird") as if it were measurement — it breaks the moment the image is compared with anything else.

---

## §5. Labels on the Image vs. the Dreaded Letter Code

Where the label sits decides whether the viewer reads or decodes.

- **Names directly on the image** tie the word to the thing. The dog group portrait labels each animal (Anna, Zerlina, Alex, Abby) in place; Bella's nine-week growth series puts the measurement labels *in the photograph where they belong* — Tufte's standard for honest scientific imaging ("Science should use Bella reporting standards"), set against astronomical images that are extensively color-processed yet "notoriously unscaled and dequantified."
- **The dreaded letter code** (A, B, C keyed to a separate list) should be avoided whenever possible. It forces the eye to ping-pong between image and legend and loses the tie between sign and referent.
- **The diagram-as-caption / profile outline** is the legitimate workaround when the image is too dense or too precious to letter directly. A traced outline placed *beside* the image (Marey's 1902 reunion: hat-and-head silhouettes carrying each scientist's name and affiliation; the dogs' profile-outline key) can hold richer captions than fit on the picture, and it can be drawn at a reduced scale to act as a compact legend. Loran's Cézanne mappings work the same way — placed *adjacent to* the painting, not overlaid on it.

| Labeling method | Use when | Cost |
|---|---|---|
| Names on the image | Few features, room to letter in place | None — preferred default |
| Profile outline / diagram beside image | Image too dense or precious to mark; captions need detail | Eye travels once to a parallel diagram, not a code list |
| Letter/number code → external legend | Truly unavoidable (extreme density) | Constant decode tax; ties broken — last resort |

**DO:** Put the name on the thing; if the image is too dense, trace a parallel outline as the legend.

**DON'T:** Default to A/B/C codes — Lichtenstein could parody Loran's earnest "DIAGRAM/A-B-C" precisely because the code-and-legend habit is so mechanical.

---

## §6. Explanatory vs. Exploratory Mapping

Whether to annotate aggressively depends on the job.

- **Explanatory presentation** (you already know what matters and are showing it): point out the important comparisons with annotations, arrows, labels, highlighting. Peterson's field guide uses pointer-line "keys" to call out the distinctive marks that separate similar birds — exactly right for teaching identification.
- **Exploratory analysis** (you are still discovering what is there): *premature* mapping diverts the viewer, forecloses alternative readings, and masks subtle detail. The analyst should look with fresh eyes and deliberately ignore the directive hints. Premature closure and "viewing-to-please" turn open analysis into advocacy and marketing.

**The both-views method (underused):** show the unmapped image *and* the mapped image — a clean look first, then what the mapping brought to it. This lets the viewer audit the mapping instead of swallowing it. Tufte says this should be done much more frequently.

**DO:** In exploration, present the clean image first; add the mapping only after the viewer (or you) has looked freshly.

**DON'T:** Pre-annotate an image you are still trying to understand — you will see only what the arrows told you to see.

### Where the mapping apparatus comes from (p. 115, adjacent chapter)

Having decided *to* map, how do you choose what apparatus to add? Tufte's rule: metaphors and analogies can genuinely assist reasoning about analytical design, **but the metaphors should derive from the content and from the reasoning associated with that content** — not from computer interfaces.

His worked positive case is the Golden Field Guide's jay spread (Robbins, Bruun & Zim, *Birds of North America*, 1966, illustrated by Arthur Singer). The task is *visual recognition of physical objects, joined to new verbal, geographic, and graphical information*, and every element of the apparatus is derived from that task:

| Apparatus element | The task requirement it answers |
|---|---|
| Painted images of each bird | Recognition of the object itself |
| A 7-bird profile-comparison strip across the top | Discriminating similar species by silhouette |
| Location maps per species | Ruling out species that do not occur where you are |
| Song scores in musical notation | Identification by ear when the bird is not visible |
| Verbal description and identifying keys | The distinguishing marks that images alone under-specify |

**The location maps are the sharpest illustration.** They earn their space by preventing a specific, nameable error class: confidently identifying a bird in **Montreal** that in fact lives only in **Acapulco**. That is what content-derived apparatus looks like — each addition eliminates a known failure of the actual task.

**The rule for §6, stated operationally:** derive the mapping apparatus from the identification or reasoning task, not from a UI pattern library. "Add a tooltip / a legend / a zoom control" are interface metaphors and answer no question the content posed. Ask instead: *what mistake will a competent viewer make with this image, and what annotation makes that mistake impossible?*

**DON'T:** Base the design of an evidence display on a computer-interface metaphor — Tufte's explicit exclusion. The apparatus should look like the subject's own reasoning, not like software.

---

## §7. Explanatory Tightness: Credible Mapping vs. Crank Mapping

The chapter's hardest and most original argument: **when a mapping makes an explanatory claim about an image, it inherits the standards of credible explanation.** A mapping can be drawn beautifully and still be worthless evidence.

### The dividing line

What separates Loran's Cézanne analyses and Hockney's optical-instrument hypothesis (perspective lines traced on Holbein's *Ambassadors* to argue divergent vanishing points imply a mirror lens) from crank work is **explanatory tightness**: their mappings are *specific, coherent, credible, and testable* — they try to explain a particular thing and could in principle be wrong. Mössel's 300+ geometric overlays (in a 534-page book claiming Ur-Forms beneath nearly all art; p. 29) are the opposite: flexible enough to fit anything, refutable by nothing — Tufte's verdict at p. 31 is that all 300 are not replicated research but the drawings of a monomaniac, and that different maps fit the same artwork because many symmetries and proportions can be claimed of any image.

> "...no possible empirical evidence can ever refute a Mössel, who explains everything and therefore nothing." — Tufte, *Beautiful Evidence*, p. 31

### Why crank mappings always "work"

- **Too many degrees of freedom.** Different grids fit the same artwork; dots could plausibly sit elsewhere; even fixed dots can be connected many ways. A scheme that fits every case discriminates none. (Feller demolished the same move in statistics: a "law of logistic growth" was fitted to populations, bacteria, railroads, plant and animal size — but normal, Cauchy, and other distributions fit the same data *as well or better*, so the logistic explained nothing distinctive.)
- **Alignment-to-please / viewing-to-please.** A registration will "lock right into place if the desired answer is already known." Tufte aligning a sculpture plate to a north marker could gain ±3° just by tilting his head; land surveyors mapping the same parcel get divergent results depending on the client's interest. **Construct the mapping independently of the result you want.**
- **The flatland–spaceland mismatch (catastrophic; p. 31).** Mössel maps a single *one-eyed flatland photograph* of a real 3-dimensional object and treats the result as a fact about the object. A photograph is not the artwork; a flatland mapping cannot capture spaceland reality. No amount of re-aligning a grid-net over one projection recovers the lost dimension.

### Test before you trust a mapping

| Question | Credible (Loran, Hockney) | Crank (Mössel, golden-section-everywhere) |
|---|---|---|
| Specific claim about a specific image? | Yes | No — universal, vague |
| Could evidence refute it? (falsifiable) | Yes | No — fits anything |
| Built independently of the wanted answer? | Yes | No — alignment-to-please |
| Maps the 3-D object, not one flat photo of it? | Accounts for the projection | Maps a single flatland image, claims spaceland truth |
| Survives connecting the marks a different way? | Yes | No — many contrary mappings fit |

**DO:** Demand a mapping be specific, coherent, credible, and testable, and build it blind to the result you hope for.

**DON'T:** Accept a mapping because it "fits" — a theory that fits everything has told you nothing; check it could have failed.

---

## §8. Mapping Motion, and Images That Map Other Images

### Motion in still-land ("movie-land")

Showing a moving thing in a static frame is inherently hard. The toolkit: directional arrows, floor plans, trace lines, linked images, and words. The 1762 contredanse pamphlet maps a dance as **small multiples** — 8 movements across a consistent grid, each cell combining figures, two floor-plans, trace-tracks, and music. Read *down* a column for the sequence within a movement, *across* for the sequence of movements; the steady repeated format is "a canvas upon which to paint, preserve, and reason about the changing information." Tufte flags its honest gap: the floor-tracks lack an explanatory legend. *How to Ski by the French Method* does the same with 200 motion-stopped photos, overlaying 2-color diagrams so the analytical variables (time, slope grade) read left to right. Good still-land strategies usually translate to actual motion graphics — design for both.

### Images mapping images

An image can map another image: a before/after history, a painting beside its forgery, similar species side by side. The photosynthesis AFM triptych maps molecular dynamics with x-y scale bars per panel and a color scale for z (depth). Tufte's own Rock/Braque/Picasso trio (each carrying a 1 cm bar) maps a fractured rock against two Cubist paintings to argue that Cubism pictures real fractured 3-D planes. The rule that makes these work is §4: even comparison images must share the universal grid, or the comparison is impressionistic.

**DO:** Use a constant repeated frame (small multiples) for sequence and motion so only the data changes cell to cell.

**DON'T:** Compare two images that lack a shared scale/grid — "looks bigger" is not a measurement.

---

## §9. Worked Example: The Vigilante (the chapter's own mapped picture)

The 1823 anti-slavery plan and cross-section of the slave ship *Vigilante* (pp. 22–23; London Religious Society of Friends, *Case of The Vigilante, A Ship Employed in the Slave-Trade*; folding plate engraved by J. Hawkesworth) is the chapter's central demonstration that a *moral* document gains force from engineering-diagram rigor.

- **Plan, elevation, and cross-section** of the ship captured off Africa in April 1822, with a **"Scale of Feet"** along the bottom and a **"Water Line"** on the section — the full apparatus of a measured drawing.
- Nearly identical human figures count out the numbers: **227 men and 120 women**, 347 people; the elevation's double layer shows the packing; the labels mark Captain's cabin and wine lockers against the human cargo.
- The facticity — individuals cumulating into an overview, hidden lines, plan views, elevations, labels, a measurement scale — gives it "the straightforward quality and credible precision of an engineering diagram," and that precision is exactly what makes it more damning than any still-life or photograph. The detail signals the ship was examined carefully, which *adds to the credibility* of the image — and of the surrounding claim about the **12,000,000 to 20,000,000** people eventually carried into America and the New World by the trade (p. 22). Tufte's own comparison on the page is to Minard's 1812 graphic: both earn their force from the straightforward quality and credible precision of an engineering diagram.

The lesson: mapping does not cool an image; the measured grid is what makes the evidence undeniable.

---

## §9b. The Designer-as-Researcher Standard (pp. 116–117, adjacent chapter)

The *Vigilante* shows what a well-mapped image achieves. This shows what production arrangement makes one possible.

Tufte's model of mapped motion is **Megan Jaegerman's "Spotting a Hidden Handgun,"** parts of which appeared in *The New York Times*, 26 May 1992. It choreographs movement in 3-space using sequences, call-outs, motion arrows, mappings, and **multiple viewpoints** — silhouette, 3-dimensional figure, and flatland footprints — with words and images working together to describe an extended causal sequence: asymmetrical gait, upper-body shift, the quick adjustment when a gun's weight shifts, running from the rain, conspicuous clothing.

**The claim that matters is not about the drawing.** Jaegerman did **both the research and the design**, breaking what Tufte calls their common alienation. The design amplifies the content *because the designer created the content* — she knew which asymmetry mattered because she had interviewed the detective, watched him act out the motions, and handled the weapons herself.

He then reproduces her **backup documentation** as evidence of the care the work required: confirmation of Detective Robert T. Gallagher's identity and record against a public database, notes on his 18 years with the NYPD and his years in the anti-robbery tactical unit, the 1,200 gun arrests and near-flawless conviction rate, and — decisively for the graphic's logic — the legal sequence from suspicious demeanor to probable cause to frisk to arrest, which is *why* the tell-tale signs shown are the ones that matter.

**The rule for this skill:** mapping quality is downstream of whether the mapper did the reporting.

| Do | Don't |
|---|---|
| Have the person who understands the content produce the mapping, or make the researcher and designer work as one unit | Hand finished findings to a designer to "visualize" — the annotations will mark what looks important, not what is |
| Keep and show backup documentation: sources, interviews, verifications, what was checked and how | Present a mapped image whose provenance chain exists nowhere |
| Let the domain's own decision logic (here: suspicion → probable cause → frisk) determine which features get annotated | Annotate the visually striking features and hope they are the diagnostic ones |

---

## §10. Failure Modes

### THE DIFFERENT-AND-UNKNOWN SCALE
**What happens:** Heterogeneous subjects are forced into identical frames (Bloch's 216 fishes in equal boxes), so each is silently rescaled and none can be compared.
**Fix:** Put every image on the universal ruler — a real scale bar per image (the redraw), never uniform framing as a stand-in for scale.

### THE DEQUANTIFIED CELEBRATORY IMAGE
**What happens:** A scientific or journalistic image is published as a beauty shot — color-processed, dramatic, and unscaled ("the marketing department"); the most extensively manipulated images (deep-space photos) are the least quantified.
**Fix:** Bella reporting standards — scale bar plus measurement labels embedded in the image; a comparison object of known size at minimum.

### THE DREADED LETTER CODE
**What happens:** Features are tagged A/B/C and keyed to a separate legend, breaking the tie between sign and referent and taxing the eye.
**Fix:** Name things directly on the image; when density forbids it, use an adjacent profile-outline diagram as the legend.

### THE FLATLAND–SPACELAND MISMATCH
**What happens:** A single flat photograph of a 3-D object is mapped and the result is claimed as a truth about the object (Mössel's grids over one-eyed photos of sculptures).
**Fix:** Map the object in 3-space — multiple viewpoints, cross-sections, x/y/z scales; never over-read one projection.

### THE UNFALSIFIABLE MAPPING
**What happens:** A scheme (Ur-Forms, golden-section-everywhere) is flexible enough to fit any image and refutable by no evidence — it explains everything and therefore nothing.
**Fix:** Require explanatory tightness — specific, coherent, credible, testable; confirm the mapping *could* have failed and survives connecting the marks differently.

### ALIGNMENT-TO-PLEASE / PREMATURE CLOSURE
**What happens:** The mapper unconsciously tilts the registration until it confirms the wanted answer (±3° free just by moving the head); or premature annotation in exploration forecloses alternative readings.
**Fix:** Construct the mapping independently of the desired result; in exploration show the unmapped image first; state alignment tolerance honestly.

---

## §11. Evaluation Checklist

Run before publishing any explanatory or evidential image.

**Scale and grid**
- [ ] A measurement scale is embedded *in* the image (not only the caption), with its conversion stated
- [ ] The scale survives reproduction/rescaling, with an explicit rescale factor if reduced
- [ ] The image sits on a universal frame (x, y, z, t as applicable), and the grid stays attached through zoom/crop
- [ ] Comparison images share one scale/grid, not relative-only sizing

**Labels and context**
- [ ] Names sit on the things they name; no A/B/C code unless density truly forbids in-place labels
- [ ] If a code/legend is unavoidable, it is a parallel outline diagram, not a bare list
- [ ] Each mark is contextualized (neighborhood + universal frame), not floating

**Explanatory integrity**
- [ ] The mapping makes a specific, falsifiable claim — name what evidence would refute it
- [ ] It was built independently of the desired answer (no alignment-to-please)
- [ ] It maps the real object, not a single flat photo treated as the object
- [ ] It still holds if the marks are connected a different way

**Mode and motion**
- [ ] Exploratory images shown clean first; aggressive annotation reserved for explanation
- [ ] Both unmapped and mapped versions offered where the mapping is contestable
- [ ] Motion/sequence uses a constant small-multiple frame; any track/legend gap is acknowledged

---

## Quick Reference: Mapping Decision Table

| Goal | Add to the image | Watch for |
|---|---|---|
| Make sizes/distances readable | Scale bar + stated conversion, or known comparison object | "Not to scale"; identical framing boxes |
| Make position comparable | External grid lighter than data; universal x/y/z/t | Grid heavier than the data it measures |
| Name parts | Labels on the things | Dreaded A/B/C letter code |
| Caption a dense/precious image | Adjacent profile-outline diagram as legend | Overlay that obscures the evidence |
| Show motion / sequence | Small multiples, constant frame, trace lines | Tracks with no explanatory legend |
| Compare two images | Shared scale/grid across both | "Looks bigger" relative-only judgment |
| Argue a theory about an image | Specific, testable, independently built mapping | Schemes that fit everything; flatland over 3-D |
| Explore an unknown image | Clean image first; minimal hints | Premature mapping, viewing-to-please |