Typography & Annotation

Text is how a chart explains itself. These rules cover the text hierarchy, axis and data labeling, number formatting, and the source line.

1 Text hierarchy

  • TY-1 (MUST) Every chart carries, in order: title (the finding, P-2), subtitle (measure, unit, geography, period), and source line (P-7). Optional between subtitle and source: axis labels, annotations, footnotes.
  • TY-2 (MUST) Title and subtitle are left-aligned at the chart’s left edge (BBC finalise_plot() convention; Economist and FT practice). Units live in the subtitle (“GDP, % change on a year earlier”), not repeated on every axis tick.
  • TY-3 (MUST) Chart text uses a single sans-serif family at web sizes that stay legible on phones. Reference scale (Urban Institute web values):
    • title ~20px bold,
    • subtitle ~16px,
    • axis and data labels ~12px,
    • legend ~14px,
    • source/notes ~11px.
    • Sentence case for all chart text; never all-caps for data labels.
  • TY-4 (MUST) All text is horizontal — no vertical or diagonal axis labels (UK Analysis Function). If category labels don’t fit horizontally, flip to horizontal bars (CT-14).

2 Titles and subtitles on the web (accessibility interaction)

  • TY-5 (SHOULD) On web pages, render title, subtitle, and source as HTML text adjacent to the graphic rather than baking them into the image — screen readers and reflow then get them for free (UK Analysis Function 1.4.5 guidance).

3 Legends vs direct labels

  • TY-6 (SHOULD) Label series directly at the line end or on the bar whenever space allows; use a legend only when direct labels genuinely don’t fit (UK AF: “don’t use legends if direct labeling is possible”; Economist: where linking lines get crowded, “key the labels with small colour block”). If a legend is used, order it to match the visual order of the series and place it above the plot (BBC default: legend at top, no legend title).

4 Axes, gridlines, ticks

  • TY-7 (MUST) Value axis: right-align numeric tick labels; use thousands separators (“121,576”); at most ~10 light-grey gridlines; label the final tick when space permits (UK AF).
  • TY-8 (MUST) Draw one strong baseline at zero (or the reference value) — BBC style #333333 — heavier than gridlines. Other chart borders and axis lines are omitted.
  • TY-9 (SHOULD) Abbreviate time axes after first mention the way newsrooms do: “1994 96 98 2000 02 …” (Economist practice); don’t repeat the century on every tick.

5 Numbers

  • TY-10 (MUST) Round to the precision the story needs — no false precision (write 4.5, not 4.5271). Keep decimal places consistent within a series.
  • TY-11 (MUST) State units once, in the subtitle or axis header: %, $bn, per 100,000 population. Symbols (%, $) don’t repeat on every tick if stated in the subtitle.
  • TY-12 (SHOULD) For scale words follow one convention: bn/m/trn abbreviations or full words, publication-wide.

6 Annotation

  • TY-13 (SHOULD) Annotate the chart where the story happens: short labels with a thin pointer at the event (“Privatisation begins” — Economist example), placed near the relevant data in dark grey/black (UK AF). An annotated chart beats a caption paragraph.
  • TY-14 (MUST) Footnote markers (*, †, ‡) attach caveats to specific values; the note text sits with the source line (“*To June 30th”).

7 Source and credit line

  • TY-15 (MUST) Bottom-left: Source: / Sources: naming the data provider(s), separated by semicolons (“Sources: Thomson Reuters; IMF”). Bottom-right MAY carry the publication credit or logo (BBC finalise_plot() places the logo bottom-right).