Tufte Visualization Ideation (PMX Canvas)

Apply Edward Tufte's principles to design clear, honest, high-density data visualizations, then realize them with PMX Canvas graph / json-render nodes. Color must encode data, not decorate.

Workflow

For new visualizations:

1. Clarify the data story
   • What comparisons matter?
   • What's the key insight to communicate?
   • Who's the audience?
2. Select approach using Tufte principles:
   • High comparison need → Small multiples (several small graph nodes, shared scale)
   • Dense data → Consider data tables (json-render Table), sparklines (Sparkline)
   • Time-series → Line charts with minimal grid
   • Part-to-whole → Avoid pie charts; prefer bar/table
   • Ranked single metric across categories → DotPlot over a bar forest
3. Design with data-ink in mind
   • Start minimal, add only what's necessary
   • Every element must earn its ink
   • Default to a single accent; use the full palette only when color encodes a variable
4. Apply the eraser test before shipping
   • For every element (label, tick, gridline, border, annotation): can it be erased without losing information that's not already conveyed elsewhere?
   • Watch for duplicate encodings: numeric labels next to a value already marked by a tick; legends duplicating direct labels; per-panel scale annotations duplicating a shared-scale caption.
   • If two elements compete for the same job, keep the visual one and drop the textual one (or vice versa) - not both.
5. Apply the collision test before shipping
   • For every text element in the plot (axis labels, point annotations, epoch labels, baseline labels, explanatory notes): mentally draw its bounding box. Does anything else - another text element, a data line, dense markers - live in or cross that box?
   • The eraser test catches redundant elements; the collision test catches crowded ones. Both must pass.
   • Standard fixes: move explanatory prose out of the plot into a nearby markdown node; relocate band/epoch labels to a dedicated strip above the plot; push baseline/reference labels to the outside margin; give each in-plot annotation a leader line so the marker and the text occupy clearly separated space.
   • Watch especially: inverted axes; shared-scale small multiples (labels stacked near zero in every panel); dense scatter (text vanishes into the dot cloud unless explicitly cleared).
6. Apply the Tufte test (see references/tufte-principles.md)

For critiquing visualizations:

1. Check graphical integrity
   • Calculate lie factor if proportions seem off
   • Verify baselines and scales (bar and area charts must start at zero)
   • Look for 3D distortion
2. Identify chartjunk
   • Decorative elements
   • Heavy grids
   • Unnecessary 3D effects
   • Moiré patterns
   • Gratuitous per-category color on a single-series chart (decoration, not encoding)
3. Evaluate data-ink ratio
   • What can be erased?
   • What's redundant?
4. Suggest improvements with specific before/after recommendations

Mapping to the PMX Canvas chart catalog

Realize these designs with canvas_render { action: "add-graph" } (graph nodes) and canvas_render { action: "add-json-render" }. The chart catalog: LineChart, BarChart, PieChart, AreaChart, ScatterChart, RadarChart, StackedBarChart, ComposedChart, plus the Tufte primitives Sparkline, DotPlot, BulletChart, and Slopegraph.

Color must encode data — the colorBy decision (single-series bar/column)

A single-series BarChart measures one variable across categories. Coloring each bar differently encodes nothing — it is decoration (chartjunk). Use the colorBy prop:

Default to series. Do not reach for category to "make it colorful." Pie/radar/stacked-bar already rotate the palette because each slice/series is a distinct variable — leave those as-is.

Tufte primitives (prefer over heavier charts)

• Sparkline — word-sized time-series, no axes/labels. Use inline in tables/dashboards and one per row to show a trajectory at a glance. Replaces "trending up / volatile" prose with the shape.
• DotPlot — ranked single metric across categories. Replaces a forest of bars: a dot per category on a shared axis. Far higher data-ink ratio than bars; sorts make the macro pattern pop.
• BulletChart — a measure against a target with qualitative bands. Replaces a gauge/dial (which is chartjunk). Use for KPI-vs-target, progress-vs-goal.
• Slopegraph — two-time-point comparison across many categories (before/after). Direct slope encodes change and rank simultaneously; labels sit at the endpoints (direct labeling, no legend). Lines default to a single neutral ink; set colorByDirection to accent rising lines and mute falling ones only when the direction is the point (and beware it editorializes — a falling error-rate is "good", a falling revenue is "bad").

Direct labeling over legends

Legends force the eye to ping-pong between key and plot (a duplicate encoding). Prefer labeling the data directly: end-of-line labels on LineChart/Slopegraph, endpoint labels on DotPlot, the highlighted bar's value on BarChart. Set showLegend: false on graph nodes when one or two series are directly identifiable; reserve legends for genuinely many overlapping series.

Small multiples over many overlapping series

When more than ~4 series would overlap in one chart, do not cram them into a single multi-color LineChart. Create several small graph nodes with an identical shared scale and consistent encoding, arranged in a grid (canvas_view { action: "arrange", layout: "grid" }, or a group). Position means the same thing in every panel; the sequence tells the macro story while each panel carries the micro detail. This is almost always better than color-coding 6+ lines.

Key Principles Reference

• references/tufte-principles.md - core principles from Visual Display of Quantitative Information: lie factor, data-ink, chartjunk, small multiples, integrity.
• references/analytical-design.md - extensions from Envisioning Information, Visual Explanations, and Beautiful Evidence: the 6 principles of analytical design, sparklines, layering & separation, micro/macro, range-frames, causality, confections. Load when designing dashboards, dense displays, sparklines, or explanatory graphics.

Quick checklist:

• Lie Factor ≈ 1.0 (no visual distortion; bars and areas start at zero)
• Maximum data-ink ratio
• Zero chartjunk (no per-category color unless color encodes a variable)
• colorBy chosen deliberately — default series (single accent + one highlight); avoid value unless the magnitude ramp earns the double-encode
• Clear labeling, direct over legend
• Answers "compared to what?"
• Shows causality or mechanism where relevant
• Multivariate (not over-reduced)
• Words, numbers, images integrated - not segregated
• Reveals multiple levels of detail (micro + macro)
• Layering: primary data dominates, secondary recedes
• Appropriate data density — Sparkline/DotPlot considered before a heavier chart
• >4 overlapping series → small multiples, not one rainbow chart