Chapter 2 · Practice 4 of 4
Format numbers and units so they read without effort
From Encoding and clutter
Why it matters
Small formatting choices decide whether a chart is read or squinted at. The Analysis Function recommends right-aligning y-axis values, using thousands separators, sans serif fonts and labelling all axes and series.
- Put units in the axis title or tick labels: "Revenue (USD millions)", "ms", "%".
- Round to the precision that matters; 12.4% is easier than 12.3871%.
- Use consistent formats across charts in the same report.
Each library has a formatter:
| Library | Thousands separator |
|---|---|
| matplotlib | ax.yaxis.set_major_formatter(StrMethodFormatter("{x:,.0f}")) |
| Plotly | fig.update_yaxes(tickformat=",") |
| Vega-Lite | "axis": {"format": ","} |