4  Text and Element Sizing

4.1 Introduction

One of the most common mistakes in figure preparation is manually adjusting text sizes element by element until they “look right.” This approach is inefficient, inconsistent, and defeats the purpose of using themes. This chapter reveals the elegant solution: control text size by adjusting figure dimensions, not font sizes.

Learning Objectives

By the end of this chapter, you will:

  • Understand how figure dimensions affect relative text size
  • Know the standard figure widths for journals (single vs. double column)
  • Learn to use base_size as the primary text sizing control
  • Understand when and how to adjust individual element sizes
  • Know the difference between DPI for vector vs. raster formats
  • Be able to create publication-ready figures at the correct size on the first try

4.2 The Key Insight

The Smart Way to Control Text Size

Don’t manually set font sizes for every element!

Instead, use smaller figure dimensions to make text appear larger relative to the plot.

Then use vector formats (SVG/PDF) for infinite resolution.

4.3 Visual Demonstration

Small canvas (3.5 × 3 inches)

Text appears large relative to plot

ggsave("sizing_small.svg", p,
       width = 3.5, height = 3)

Large canvas (7 × 6 inches)

Text appears small relative to plot

ggsave("sizing_large.svg", p,
       width = 7, height = 6)

4.4 base_size Effect (theme_classic(base_size = x))

`geom_smooth()` using formula = 'y ~ x'
`geom_smooth()` using formula = 'y ~ x'

base_size = 8

base_size = 11 (default)

base_size = 14

Other elements scale relative to base_size:

  • axis.title: 1.1× base_size
  • axis.text: 0.8× base_size
  • legend.text: 0.8× base_size

Use base_size as the PRIMARY adjustment - only customize individual elements if needed

4.5 The Right Workflow

Three-Step Process
  1. Set dimensions to match final output size
    • Journal single column: ~3.5 inches (Always check specific journal guidelines!)
    • Journal double column: ~7 inches
    • Presentation: ~10 inches
  2. Adjust base_size if needed
    • Only fine-tune if text still too large/small
  3. Adjust individual elements if needed
    • Use theme() to customize specific text sizes
    • Only if steps 1-2 don’t achieve desired result

Why This Works

  • Text/points/lines have fixed sizes
  • If the canvas is small they appear larger

4.6 When you must adjust some sizes individually

Default (base_size = 11)

p + theme_classic(base_size = 11)

With manual adjustments

p + theme_classic(base_size = 11) +
  theme(
    axis.title   = element_text(size = 14, face = "bold"),
    axis.text    = element_text(size = 12),
    legend.title = element_text(size = 12, face = "bold"),
    legend.text  = element_text(size = 11)
  )

4.7 Vector vs Raster: Key Differences

Vector Formats (SVG, PDF)

Dimensions control text/element proportions, not quality!

  • Scale infinitely without quality loss
  • DPI is ignored
  • What matters: aspect ratio & relative proportions
# Text larger in small.svg
ggsave("small.svg", p,
       width = 3.5, height = 3)
ggsave("large.svg", p,
       width = 7, height = 6)
Raster Formats (PNG, TIFF)

DPI controls pixel count and quality!

  • Fixed resolution, can pixelate when scaled
  • DPI matters (300+ for print)
  • pixels = width × DPI
# 1500×1200 pixels
ggsave("plot.png", p,
       width = 5, height = 4, dpi = 300)
# 360×288 pixels
ggsave("plot.png", p,
       width = 5, height = 4, dpi = 72)

4.8 Summary

Key Takeaways
  1. Size figures to match final output - not to match your screen
  2. Standard journal widths:
    • Single column: ~3.5 inches (check specific journal!)
    • Double column: ~7 inches
    • Presentation: ~10 inches
  3. Use base_size as primary control - all theme elements scale proportionally
  4. Smaller canvas = larger text - text is fixed size, reducing plot area makes it relatively larger
  5. Vector formats ignore DPI - SVG/PDF scale infinitely, dimensions control proportions
  6. Raster formats need high DPI - PNG/TIFF at 300+ DPI for print quality
  7. Manual adjustments last - only customize individual elements if dimensions + base_size aren’t enough
  8. Test at final size - view your saved figure at actual publication size to check readability

4.9 Exercises

Try It Yourself

  1. Create a plot and save it at three different widths:

    p <- ggplot(mtcars, aes(mpg, hp)) + geom_point() + theme_classic()
ggsave("single_col.pdf", p, width = 3.5, height = 3)
ggsave("double_col.pdf", p, width = 7, height = 5)
ggsave("slide.pdf", p, width = 10, height = 6)

  2. Open each PDF and compare text sizes - notice how smaller canvas makes text appear larger

  3. Try different base_size values (8, 11, 14, 18) at the same figure dimensions

  4. Create a PNG at the same dimensions but different DPI values (72, 150, 300)

  5. Look up your target journal’s figure requirements - what are their single/double column widths?

4.10 Further Reading