SQL, data modeling, data quality, EDA, visualization · insight-0068
Choose the chart from the comparison the reader must make, not from the data type
- Evidence type
- practitioner heuristic
- Difficulty
- easy
- Roles
- Data analyst, Data scientist
- Industries
- aviation, cross-industry
Summary: situation, action, reason, boundary
Situation
You need to show revenue share by fare level across three markets and the default tool suggests three pie charts.
Action
Write the comparison in one sentence ("compare high-fare share across markets"), then pick the encoding that puts those values on a common scale: side-by-side bars for comparing parts, stacked bars for parts of a whole across conditions, a line for change over time. Use pies only for two or three simple parts.
Reason
Charts are read most accurately when the compared values share an aligned axis; pies and stacked segments make readers compare angles or floating lengths.
Boundary
Reports, dashboards and slides.
Symptom or risk
Readers cannot compare slice sizes across pies, so the key message (one market relies on high fares) is lost.
Exceptions
A single part-to-whole message with few parts can work well as a pie or a stacked bar.
Trade-offs
The most accurate chart may look less familiar to some audiences.
Pitfalls
Adding more series to one chart instead of choosing which comparison matters.
Lessons and concepts
Claims and their sources
Pie charts work best for simple fractions and small datasets, stacked bars suit comparisons across conditions but make non-baseline segments hard to compare, and side-by-side bars are best for comparing individual fractions directly.