Choosing the right chart — Examples

Example 1 — The eight-slice pie no one can read

A report shows traffic by channel as a pie with eight slices, six of them close in size. Readers cannot name the largest channel without studying the angles. Re-form the chart so the comparison takes a glance, and state the question it answers.

Traffic by channel (pie)
  Direct   21%    Search   19%    Email    14%    Social  12%
  Referral  9%    Display   8%    Affiliate 7%    Other   10%

Solution

Question: "Which channel sends us the most people?"

Sorted bars, by value
  Direct    21
  Search    19
  Email     14
  Social    12
  Other     10
  Referral   9
  Display    8
  Affiliate  7

Naming the question first picks the form: bars are read by length, so a ranking is instant, whereas angles in a pie are estimated poorly and cannot be ordered. Sorting by value rather than alphabetically turns the chart into that ranking instead of a scan. The failure to avoid is choosing the form before the question — a pie this crowded answers something nobody asked and hides the one comparison that matters. Keep pies for two or three slices of a single whole.

Example 2 — A line connecting things that have no order

A dashboard draws orders per city as a line chart, which implies the cities follow one another. There is no sequence between them. Re-form it so the comparison is honest, and label the figures as illustrative.

Orders by city (line chart)
  Bristol, Leeds, London, Manchester, York
Illustrative figures: 240, 180, 420, 310, 90

Solution

Question: "Which city orders the most?"

Bars, sorted by value (illustrative figures)
  London      420
  Manchester  310
  Bristol     240
  Leeds       180
  York         90

Bars compare unrelated categories by length, while a line’s slope asserts a trend that does not exist here; sorting by value makes the ranking readable without scanning the axis. A well-formatted table would also be a legitimate answer if readers needed the exact numbers. The common failure is keeping the line because the data arrived in a spreadsheet row — the form is chosen by the question, never by the shape of the input.