Different questions call for different charts. Matching them well is most of the job.
Comparing Values
Bar charts (horizontal for long labels). Sort bars by value unless categories have a natural order.
Showing Trends Over Time
Line charts, with time on the horizontal axis. Use bars for a small number of discrete periods. Avoid too many lines; highlight the important ones.
Showing Distributions
- Histograms for one variable.
- Box plots or violin plots to compare distributions across groups.
- Density plots for smooth shapes.
Showing Relationships
- Scatter plots for two numeric variables; add a trend line if helpful.
- Heatmaps for correlation matrices or values across two categories.
Showing Composition
- Stacked bars for composition across categories or time.
- Pie or donut charts only with a few parts (ideally two to four), when the whole matters.
- Treemaps for hierarchical composition.
Showing Geography
Choropleth maps colour regions by value — normalise by population or area so large regions don't dominate. Point maps for locations.
Frequently Misused
- Pie charts with many slices.
- Line charts for unordered categories.
- Stacked areas where the middle layers are impossible to read.
- Maps when geography isn't the point.
When in Doubt
A simple sorted bar chart or a clear table is rarely wrong.