Choose the right chart for the question

Bisi has been reading your tables for six modules. She is patient, but tables make people work: the reader has to hold numbers in their head and do the comparing themselves.

A chart does the comparing for them. That is its entire job, and it explains why choosing the wrong one is so damaging — a chart that answers a different question than the one asked is worse than no chart at all, because it answers confidently.

Before you draw anything, finish this sentence: "I want the reader to see that…"

If you can't, no chart will help. If you can, the chart almost picks itself.

Words in this lesson

Five questions, five charts

Almost every business chart answers one of five questions.

Learn those five and you can chart almost anything a small business needs.

Making one in Google Sheets

According to Google's help centre: select the cells you want to include, then click Insert → Chart. Double-click a chart to open the editor, which has a Setup tab for the data and a Customize tab for the appearance.

Google's documented chart types include Line, Combo, Area, Column, Bar, Pie, Scatter, Histogram, Candlestick, Organizational, Tree map, Geo, Waterfall, Radar, Gauges, Annotated timeline and Table.

Note Google's distinction, which people get wrong constantly: Column is vertical, Bar is horizontal. They are different chart types in the menu.

In Excel, it's Insert → Charts, with the same families.

1. Change over time: line

Jan  3,115,850
Feb  3,814,350
Mar  4,096,100
Apr  5,022,750
May  4,506,750
Jun  4,954,550

A line chart shows the shape of that immediately: rising, with a dip in May. You feel the May dip in a way you don't reading six numbers.

Rules for line charts:

• Time goes on the horizontal axis, left to right, always.
• Don't skip periods. If a month has no data, show the gap; don't close it up.
• Three or four lines maximum. Beyond that nobody can follow them.
• The value axis normally starts at zero — but see lesson 7.2, because this is the one rule with a real exception.

Don't use a line for categories. A line between "Yaba" and "Ikeja" implies something continuous between them, and there is nothing between two shops.

2. Comparison: bar or column

Yaba      5,586,900
Ikeja     3,604,550
Surulere  1,834,850

The most useful chart in business, and the most underused, because people reach for a pie instead.

Rules for bar charts:

• Sort by value, unless the categories have a natural order like months. Bisi's branches sorted largest-first are readable at a glance; alphabetical order makes the reader search.
• Use horizontal bars when the labels are long. "Baking and sweeteners" fits comfortably beside a horizontal bar and gets truncated or rotated under a vertical one.
• Start the value axis at zero. Always, for bars. A bar's length is the message.
• Add data labels when there are few bars. The reader gets the picture and the precise number at once.

And the caveat this course keeps returning to: before comparing three branches, check they are comparable. Surulere's bar covers two months against the others' three.

3. Composition: stacked bar, and the pie problem

Bisi's Q1 payments:

Three parts of a whole. A pie chart is defensible here — just.

Now her categories:

A pie of this is a bad chart. Seven slices, and the bottom three are 5.2%, 3.2% and a sliver each — indistinguishable wedges the reader cannot rank. A sorted horizontal bar chart shows the same seven numbers in an instantly readable order.

When a pie is acceptable:

• Two to four parts
• They genuinely sum to a meaningful whole
• The differences are large
• You want "roughly half" rather than precise comparison

When it isn't: more than four slices, similar-sized slices, comparing two pies to each other, or anything where the reader needs to rank the parts.

If you need composition and change over time, use a stacked column per month. If the reader needs to compare the parts rather than the total, use separate lines instead — stacked segments above the bottom one are very hard to compare, because they all start at different heights.

4. Spread: histogram

From lesson 4.2, Bisi's sale sizes are heavily skewed: median ₦4,950, mean ₦11,755, maximum ₦86,500.

A histogram shows that shape in one picture: a tall block of small sales at the left, a long thin tail stretching right. It is the chart that makes "mean and median differ" obvious rather than something you have to explain.

Google lists Histogram as a chart type. It groups values into buckets automatically, or you can set the bucket size yourself.

Use a histogram whenever you're about to quote an average. If the shape is lopsided, your reader needs to see it, and it takes thirty seconds to find out.

5. Relationship: scatter

One dot per record, two numbers per dot.

In lesson 4.5 you found that quantity and sale value correlate at just 0.051 — almost no relationship. A scatter plot shows why instantly: a vertical stripe of ₦86,500 rice bags at quantity 1, and a spread of small values at quantities 5 to 7. The picture explains the number.

Rules for scatter plots:

• The thing you think is the cause goes on the horizontal axis.
• With many overlapping points, make them semi-transparent or smaller.
• A trend line is fine — Google documents adding one — but lesson 4.5 still applies: a trend line is a description, not a prediction, and never evidence of cause.

The charts to avoid

Google's help does document a second Y-axis: double-click the chart, click Customize → Series, choose the series, and under Axis choose Right axis. It exists and it is occasionally right — for the same quantity in two units, say. It is almost never right for two different quantities, because you are choosing the scales that make the lines appear related.

The title does half the work

The single highest-value change you can make to any chart:

Write the finding in the title. A reader who sees only the title should still learn something true. If you can't write such a title, you may not have a finding yet — and that's worth discovering before the meeting rather than in it.

Keep the axis labels too. A title stating the finding and axes stating the units is a complete chart.

Common mistakes

The short version

• Five questions, five charts: change over time → line, comparison → bar, composition → stacked bar or a small pie, spread → histogram, relationship → scatter.
• Google: Insert → Chart, then Setup and Customize. Column is vertical; Bar is horizontal.
• Sort bars by value, use horizontal bars for long labels, and start the value axis at zero.
• A pie needs 2–4 parts. Bisi's seven categories need a bar chart; her three payment types could take a pie.
• Draw the histogram before quoting an average.
• Avoid 3D, radar, gauges and dual axes — with dual axes you pick the scales, and therefore the apparent relationship.
• Put the finding in the title. "Yaba takes half of all revenue", not "Revenue by branch".

Try it yourself

1. Write the sentence "I want the reader to see that…" for each of Bisi's three decisions from Module 5, then name the chart each one needs.
2. Build a line chart of the six monthly totals. Give it a title stating a finding.
3. Build a sorted horizontal bar chart of the seven categories, then build the same data as a pie. Write two sentences on which is easier to read and why.
4. Build a histogram of Q1 sale amounts. Mark where the mean (₦11,755) and median (₦4,950) fall, and write one sentence about the shape.
5. Build a scatter of quantity against sale amount. Explain in one sentence what it shows about the 0.051 correlation.
6. Take any chart you've made and rewrite its title three times, each stating a different true finding. Pick the most useful one.
7. Find a chart in a newspaper or company report this week. Name its chart type, the question it answers, and one thing you'd change.

You'll know you've got it when you can name the right chart before opening the spreadsheet, and your chart titles are sentences rather than labels.