Legend Styling: Highlight What Matters
Legends bridge the gap between data and perception — they help viewers decode colors, shapes, and lines at a glance. But a cluttered or confusing legend can break that connection fast.
You’ll learn how to customize legend placement, direction, titles, spacing, and keys with guides() and theme(). By the end, your legends will complement your story instead of competing with it.
👑 The Birth of a Legend
The legend translates your visual mappings into meaning, showing what each encoding like color, shape, or linetype stands for. Like a good map key, it helps readers find their way through your plot.
ggplot2 creates legends automatically whenever you map an aesthetic like color, shape, or linetype. If not specified explicitly, the legend will appear on the right of the panel, centered, and with a vertical orientation.
This is where legend styling comes in. You can shape legends from three different “spots” in ggplot2 — each handling a different layer of control:
- →In discrete legends these appear as keys, while in colorbars and binned legends they are shown as tick marks.
scale_*()
Control the labels and values that appear in the legend: how many there are, their order, what they display, and how they’re formatted — including fully overwriting labels if desired.We already talked about adjusting a scale's
name,breaks,labels,values,limits, and more in the dedicated Scales lesson. theme()Modify the overall style: where the legends are placed, whether their orientations, and visual details like spacing, margins, and text justification or alignment. Changes apply to all legends.You’ve seen some of these legend tweaks already in the Theme Attribute Explorer and in exercise 3 of the Custom Themes lesson.
guide_*()Fine-tune layout and appearance: number of rows or columns, reversing order, or even overriding aesthetics (for example, making small points appear larger in the legend).Specifythemeoptions inside the guide to customize a single legend without affecting the others.
Style a legend with...
Customize legend titles and labels: replace species names with full Latin names, set custom tick marks, and label body mass values with units.
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