Label categories directly beside the marks

Label categories next to the marks they describe instead of making readers look back and forth to a separate legend. For example, remove the color key and place series names at the ends of lines or next to pie and donut segments, and add hand-placed annotations when you need extra direct labels.

Readers understand a chart faster when the explanatory text sits where they need it. A separate legend forces repeated eye movement away from the marks and back again.

Mechanism: Direct labels shorten the distance between a category name and its encoded mark, so readers spend less effort matching colors or shapes to meaning.

Evidence: The source explicitly recommends removing the color key and labeling categories directly on the chart, with line, pie, and donut charts given as examples and annotations suggested for additional hand-placed labels. (Muth, 2022)

• User Goal: Identify which mark belongs to which category quickly.
• Task: Read category-to-mark mapping without consulting surrounding text.
• Data: Multiple categories are distinguished by line, slice, color, or similar marks.
• Chart Setting: The chart has enough room to place labels near marks.
• Audience: Readers are scanning rather than studying a long explanation first.
• Success Criterion: Readers can name each visible category without repeatedly consulting a legend.

Break it when: The layout is so tight that labels cannot fit near the marks, especially on mobile. Why: The source notes that space can be too constrained for direct labels, so a color key may need to remain at the top.

Sacrifice: You give up some plotting space to place labels inside the chart area.
Risk: In a tight layout, direct labels can stop fitting cleanly.
Mitigation: Keep direct labels where they fit, and fall back to a top legend in very tight layouts.

Mistake: Leave category names only in a separate legend or description. Why it fails: Readers must keep shifting their eyes away from the marks and may lose the explanation before returning to the data.

Failure Sign: Readers must repeatedly glance between a legend and the marks to decode categories.
Quick Check: Hide the legend and see whether each visible mark still says what it is.
Stronger Test: Ask whether the category name appears at the mark itself or only somewhere else on the page.

• Remove the legend when the categories can be named directly on the chart.
• Place category names next to the specific lines, slices, or other marks they describe.
• Add annotations by hand when a category needs a direct label that the default layout does not provide.
• Keep a top legend only when the layout is too tight for direct labels.