Match the chart type to the question: comparison, change over time, distribution, relationship or part-to-whole.
Why it matters
"What chart should I use?" is the wrong first question. The right first question is "what does my reader need to find out?" Once you can name the question, the chart type nearly chooses itself. Most business and research questions fall into five families, and each family has one or two charts that answer it well.
The five question families
| Question | Example | Good first choice | Also consider |
|---|---|---|---|
| Comparison across categories | Which product sold most? | Bar chart (horizontal if labels are long) | Dot plot, lollipop chart |
| Change over time | How did monthly sign-ups change? | Line chart | Column chart for few periods, area chart for totals |
| Distribution | How long do deliveries usually take? | Histogram | Box plot, density plot, strip plot |
| Relationship between two measures | Do longer sessions mean more purchases? | Scatter plot | Scatter with trend line, bubble chart, heatmap for many points |
| Part-to-whole | What share of revenue comes from each channel? | Stacked bar (100%) or simple bar of shares | Pie only for 2 to 3 slices; treemap for hierarchies |
A sixth family, geography ("where?"), uses maps, but only when location itself matters. A map of sales by state is often better as a sorted bar chart, because large, empty states dominate a map visually.
Worked examples
1. "Which of our 12 support teams resolves tickets fastest?" This is a comparison across categories. Use a horizontal bar chart of median resolution time, sorted from fastest to slowest. Sorting matters: an alphabetical order forces the reader to hunt for the ranking.
2. "Is our weekly active user count growing?" Change over time, so use a line chart with weeks on the x-axis. Time almost always goes left to right. If you have many series (say one per country), do not draw 30 tangled lines; highlight one or two and grey the rest, or use small multiples (Module 2).
3. "Are most orders small, or do a few large orders dominate?" A question about distribution, so use a histogram of order value. An average alone would hide the shape: a mean of 50 could come from many orders near 50, or from many orders near 10 plus a few at 500. If you need to compare distributions across several groups, side-by-side box plots save space.
4. "Do customers who use the app more spend more?" Relationship, so use a scatter plot with usage on x and spend on y. Each dot is one customer. With thousands of points, reduce dot opacity or use a 2D histogram so overlapping points remain visible. Remember that a pattern shows association, not cause.
5. "What share of support tickets come from each channel?" Part-to-whole. With three channels a pie can work, but a bar chart of percentages sorted descending is easier to read, and it still works with eight channels. To show how the mix changes over time, use a 100% stacked bar per month, and put the most important category on the baseline so its changes are easiest to read.
Tables are allowed
When readers need to look up exact values ("what was March revenue in Spain?"), a well-formatted table beats any chart. Charts show shape and pattern; tables show precise values. A dashboard often needs both.
Questions to ask before you pick
- What is the one question? Write it as a sentence. If you have three questions, you may need three charts.
- What type is each variable? Categorical (region), ordinal (small, medium, large), continuous (revenue), or time.
- How many categories or points? Five bars are easy; 50 bars need sorting, grouping or filtering.
- Who is reading, and where? An executive skimming a slide needs one obvious message. An analyst exploring in a notebook can handle a dense scatter matrix.
Common mistakes
- Line charts for categories. A line implies continuity, so connecting "Sales, Marketing, Support" with a line suggests a trend that does not exist.
- Pie charts with many slices. Beyond three or four slices, angles become impossible to compare.
- Dual y-axes. Two scales on one chart let you make any two series look correlated by stretching one axis. Use two aligned charts instead.
- Unsorted bars. Sort by value unless the categories have a natural order (months, age bands, survey scales).
- Choosing for novelty. Radial charts, word clouds and Sankey diagrams look impressive but are hard to read accurately. Use them only when their special strength (flows for Sankey, for example) is the point.
Quick recap
- Start from the reader's question, not the chart gallery.
- Comparison: bars. Time: lines. Distribution: histograms or box plots. Relationship: scatter. Part-to-whole: sorted bars or 100% stacked bars.
- Sort categories, keep time left to right, and use a table when exact values matter.