Be aware of points plotted exactly on top of one another

Technical term for this problem: overplotting

Partial transparency helps highlight overlapping points

A little jitter shows overlaps even more clearly

But don't jitter too much

Contour lines are the 2D version of density plots

We can vary shading for added effect

What do we do when there are multiple groups?

Colored contour lines can work for 2 to 3 groups

What if there are multiple groups intermingled?

Don't make plots that look like spaghetti

Contour lines work well with small multiples (facets)

2D histograms: rectangular bins

2D histograms: rectangular bins

2D histograms: hex bins

2D histograms: hex bins

Choosing the right color scale

Choosing the right color scale

Choosing the right color scale

Choosing the right color scale

Choosing the right color scale

Choosing the right color scale

Choosing the right color scale

Contour lines

blue_jays %>%
  ggplot(aes(body_mass_g, head_length_mm)) +
  geom_point() +
  theme_bw(14)

Contour lines

blue_jays %>%
  ggplot(aes(body_mass_g, head_length_mm)) +
  geom_density_2d() +
  geom_point() +
  theme_bw(14)

Contour lines

blue_jays %>%
  ggplot(aes(body_mass_g, head_length_mm)) +
  geom_density_2d(bins = 5) +
  geom_point() +
  theme_bw(14)

Contour bands

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_density_2d_filled(bins = 5) +
  #
  geom_point() +
  theme_bw(14)

Contour bands

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_density_2d_filled(bins = 5, alpha = 0.5) +
  #
  geom_point() +
  theme_bw(14)

Contour bands

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_density_2d_filled(bins = 5, alpha = 0.5) +
  geom_density_2d(bins = 5, color = "black", size = 0.2) +
  geom_point() +
  theme_bw(14)

2D histograms

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_bin2d() +
  theme_bw(14)

2D histograms

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_bin2d(binwidth = c(3, 3)) +
  theme_bw(14)

2D histograms

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_bin2d(binwidth = c(1, 5)) +
  theme_bw(14)

2D histograms

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_bin2d(binwidth = c(5, 1)) +
  theme_bw(14)

Hex bins

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_hex() +
  theme_bw(14)

Hex bins

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_hex(bins = 15) +
  theme_bw(14)

Hex bins

ggplot(blue_jays, aes(body_mass_g, head_length_mm)) +
  geom_hex(bins = 10) +
  theme_bw(14)

Further reading

• Fundamentals of Data Visualization: Chapter 18: Handling overlapping points
• ggplot2 reference documentation: geom_density_2d()
• ggplot2 reference documentation: geom_bin2d()
• ggplot2 reference documentation: geom_hex()