Scatter plot encodes values as position of points on two quantitative axes. John Herschel plotted orbits; Galton’s 1880s regressions made the form famous.
In reports, ads and assignments it fits correlation, outliers and clusters in two measures. Skip it when one axis is not quantitative, or time is the real story.
Rules
- Rules 1 — Use position of points on two quantitative axes as one channel, not two.
- Rules 2 — Direct labels beat a distant legend.
- Rules 3 — Do not hide zero. If you break the axis, say so.
- Rules 4 — Colour encodes category or magnitude, not both.
- Rules 5 — Put the claim in the title, not just “Scatter plot”.
- Rules 6 — Source and period, even in small type.
Palette
- Palette 1 — Categories: distinct hues. Sequences: one hue, changing value.
- Palette 2 — Diverging: a neutral centre, emphasis at both ends.
- Palette 3 — One brand colour plus greys beats a rainbow.
- Palette 4 — Check contrast on a projector and in greyscale print.
Type
- Type 1 — Tabular figures for numbers. Do not pour body copy into the chart.
- Type 2 — Titles as sentences; axes as short nouns.
- Type 3 — For CJK, drop weight one step and leave tracking.
Scatter plot: honour position of points on two quantitative axes, and switch when one axis is not quantitative, or time is the real story.