Chart Selection¶
Match the chart to the question.
Pick a chart by goal¶
Start with what you want to show. Click a goal to see chart options that fit, with the typical use case and common pitfalls.
Decision flow¶
- What is the question? Comparison, trend, distribution, composition, relationship, geographic
- How many variables? 1, 2, or many
- What data type? Numeric, categorical, time, geographic
Chart types¶
| Name | Use | When |
|---|---|---|
| Bar graph | Compare values across categories | Discrete categories on X; values on Y |
| Bar chart (horizontal) | Rank data | Long category labels; many categories |
| Line graph | Show changes over time | Continuous time on X |
| Area chart | Cumulative trend | Magnitude + trend |
| Pie chart | Part-of-whole | ≤ 4 slices, sums to 100% |
| Donut chart | Part-of-whole | Same as pie; better label space |
| Map (choropleth/symbol) | Geographic distribution | Region/country/state data |
| Histogram | Distribution of one variable | Bin frequency of values |
| Box plot | Distribution + outliers | Compare distributions across groups |
| Heatmap | Magnitude across two dimensions | Matrix of values |
| Scatterplot | Relationship between two variables | Correlation, clusters, outliers |
| Bubble chart | Three variables (x, y, size) | Scatter + magnitude |
| Sankey | Flow between stages | Funnel, energy, traffic |
| Treemap | Hierarchical part-of-whole | Nested categories |
| Waterfall | Sequential additive change | Variance breakdown |
Choose by question¶
| Question | Chart |
|---|---|
| "How does X compare across categories?" | Bar |
| "How has X changed over time?" | Line |
| "What's the distribution of X?" | Histogram, box plot |
| "How does X break down?" | Stacked bar, treemap |
| "Is X related to Y?" | Scatter |
| "Where is X happening?" | Map |
| "How does X flow through stages?" | Funnel, Sankey |
Common mistakes¶
- Pie charts with > 4 slices → use bar chart
- Truncated y-axis → exaggerates differences
- 3D charts → distort perception
- Too many colors → audience can't parse
- Dual y-axes → easy to mislead
Color¶
- Sequential — single hue, varying lightness (for ordinal/quantitative)
- Diverging — two hues from neutral (for centered scales: e.g. -100% / +100%)
- Categorical — distinct hues (for unordered categories)
- Test for color blindness (ColorBrewer)