What it is
A column chart draws one vertical bar per category, rising from a common baseline. Because every bar starts at the same line, your eye compares their tops — position along a common scale, which is the comparison people make most accurately (Cleveland & McGill 1984).
With several measures per category, the bars stand side by side in groups, one colour per measure. That is a grouped or clustered column chart.
✓ Use it when
- You are comparing amounts across up to a dozen or so categories: sales by region, votes by option, visitors by month.
- The categories are short labels that fit under a bar, or periods in time (months, quarters, years) with only a few of them.
- You want each individual value to be easy to read and compare.
✗ Avoid it when
- There are many categories or long names — a horizontal bar chart keeps the labels readable.
- You have a long time series of dozens of points — a line chart shows the trend instead of a picket fence.
- The values are parts of one whole and the share is the message — consider a stacked or 100% chart, or a doughnut for a few parts.
Tips for a better chart
- Start the value axis at zero. A bar’s length is its value; cutting the axis exaggerates differences.
- Sort the bars by value unless the categories have a natural order of their own, such as months or age groups.
- Use one colour for one measure. Colouring each bar differently suggests a meaning the data does not have.
- Label the bars directly when there are few of them, and drop the gridlines you no longer need.
The maths
A column’s height is proportional to its value: with an axis from 0 to M drawn over H pixels, a value v is drawn H·v/M pixels tall. That proportionality is why the baseline must be zero — with an axis starting at m > 0 the drawn ratio of two bars becomes (a − m)/(b − m) instead of a/b.
Chart Buffet picks “nice” tick steps — 1, 2, 2.5 or 5 times a power of ten — so gridlines land on round numbers people can read off.
A little history
The Scottish engineer and political economist William Playfair published the first bar chart of real data in The Commercial and Political Atlas (Playfair 1786): Scotland’s imports and exports with seventeen countries for a single year, drawn as horizontal bars because, unusually, he had no time series to plot.
Bar charts spread through statistical atlases in the nineteenth century and became the default chart of business reporting in the twentieth. Cleveland and McGill’s experiments later gave the reason they work so well: judging position along a common scale beats judging angles or areas (Cleveland & McGill 1984).
Questions
What is the difference between a column chart and a bar chart?
Only the orientation. Columns are vertical, bars are horizontal. Use bars when you have many categories or long labels.
Should a column chart always start at zero?
Yes. The length of a bar encodes its value, so a truncated axis misrepresents the comparison. If small differences matter, show them with a line or dot chart instead.
References
- Playfair, W. (1786). The Commercial and Political Atlas. London: Debrett, Robinson and Sewell.
- Cleveland, W. S. & McGill, R. (1984). Graphical perception: theory, experimentation, and application to the development of graphical methods. Journal of the American Statistical Association 79(387), 531–554.
- Friendly, M. & Denis, D. J. (2001). Milestones in the history of thematic cartography, statistical graphics, and data visualization. Web document.