# Choosing a form Decide this **before** color. The data's job picks the form — and sometimes the right form is not a chart. ## Is it even a chart? | The data is… | Use | Not | |---|---|---| | A single current value (+ maybe a trend) | **Stat tile** (value + delta + sparkline) | A one-bar bar chart | | A handful of headline numbers | **KPI row** of stat tiles | A grouped bar chart | | The one number a dashboard leads with | **Hero figure** (≥48px, sans) | — | | A single ratio against a limit | **Meter** (same-ramp track) | A pie of 2 slices | | More than ~7 classes that all carry meaning | A **table** (or table + chart) | More colors | If a chart *is* right, pick the type by the job: ## The job → the type | Job (what the reader must do) | Default form | Color job | |---|---|---| | Compare magnitude, low → high | bar / column; **heatmap** for a grid | sequential (one hue) | | Trend over time | line; area for a single series | sequential or 1 categorical | | Tell distinct series apart | grouped/stacked bar, multi-line | **categorical** | | One series is the point, rest are context | **emphasis** (highlight one, gray the rest) | 1 hue + gray | | Above/below a baseline; Δ to target | diverging bar, or line vs baseline | diverging | | Part-to-whole | **stacked bar** (go horizontal for many / long-named categories) | categorical | | Ordered-scale share (Likert, sentiment, agree↔disagree) | **diverging stacked bar**, centered on neutral | diverging | | Before → after per item | dumbbell | 1 hue, 2 shades | ## The rules behind the table - **Sequential is the safe default.** One hue, more-is-darker. It stays legible and consistent and is hard to misread. Reach for it unless the data's job is specifically *identity* or *polarity*. - **Categorical is for when the series ARE the subject** — and it has a real cost: it can bury the one data point that actually matters. If the story is "this one went up," that's **emphasis**, not categorical. - **Emphasis** = the most underused form. One series in the accent hue, the rest in the de-emphasis gray. Often the honest answer to "make this chart clearer." - **Texture is an opt-in expression, not a default form.** It earns its place only for accessibility (full CVD), print/export, and `forced-colors`. Never decorative. → see `marks-and-anatomy.md`. ## Series-count ladder (categorical) | Series | Treatment | |---|---| | 1–3 | color alone is comfortable for everyone; direct-label | | 4 | the CVD floor enters — direct labels become mandatory, not a courtesy | | 5–6 | soft cap; legend or small multiples | | 7–8 | token ceiling; past it, fold the tail into "Other," facet into small multiples, or use composite encoding (hue × shape) | Never solve "too many series" by generating more hues. A generated 9th hue is indistinguishable from an existing one under CVD and breaks every check.