Level 5 · Parts of a whole, without the pie

When a pie works

A pie shows parts of one whole, and it works in a narrow case: two or three slices, one of them clearly dominant, and a reader who only needs “most of it” or “about a quarter”. “43% of 2025 revenue came through the app” is a fine two-slice pie.

It stops working as soon as slices are close or numerous. People judge angles and areas poorly, so Harbor & Pine’s 2025 shares (Furniture 24.9%, Outdoor 22.1%, Lighting 16.7%, Kitchen 12.7%, Decor 12.6%, Textiles 10.9%) become six similar wedges. Kitchen and Decor differ by 0.1 points; no one can see that in a pie, everyone can in chart B.

Sorted bars for shares

A bar per category, sorted from largest to smallest, on an axis that starts at zero, answers “which is biggest and by how much” with the most accurate comparison the eye can make: lengths from a common baseline. Label each bar with its percentage and the chart needs no legend.

Stacked columns and what they hide

Stacked columns (chart A) show the mix of each year side by side, and they are good for “what does the whole look like, and roughly how is it split?” The trap is reading change from them. Only the bottom segment starts at zero in every column. Every other segment floats on the ones below it, so a segment that grew can look flat when the one under it shrank. When the question is change, compute the change and chart it: points gained or lost per category, sorted.

Combo charts and the second axis

A combo chart puts columns and a line on one chart, often with a second y axis on the right (quantity sold as columns, average price as a line, say). The two scales are independent, so whoever makes the chart decides where the lines cross and how steep each looks. Two measures with different units belong in two charts side by side, or on one chart after indexing both to a common base (2023 = 100).

Comparing many metrics: radar or small multiples

A radar chart compares groups on several metrics at once, one spoke per metric. Its area changes with the order of the spokes, and the metrics share one radial scale even when their units differ. Small multiples, one simple bar chart per metric with the groups in the same order, carry the same comparison and can be read exactly.

Common mistakes

• A pie because it “adds to 100%”. Use it only for two or three clearly different slices.
• Reading change from floating segments. Compute the change and chart it.
• A second y axis. Two units, two charts, or index them to a common base.
• Unsorted bars. Alphabetical order makes the reader do the ranking.