Overview

Teaching: 10 min
Exercises: 10 min

Questions

• What kind of scientific question does a bubble chart address?

• How do I generate a bubble chart with ggplot2?

Objectives

• To generate a bubble chart using ggplot2

Lead students to walk through decision making steps from question to chart.

• “What is the relationship of GDP per capita, life expectancy, and population across the world per country in 2007?”
• Relationship with three variables (at least two are continuous)
• Bubble Chart

Implement bubble chart.

• geom_point()
• geom_smooth()
• scale_manual()

Bubble Chart Sort and Fill-in Challenge

Sort and fill in the missing pieces of the following code to generate a bubble chart.

ggplot(data, aes(x = ________, y = ________, size = pop_2007)) +
geom_point() +
theme_classic()
geom_smooth() +
labs(x = ________, y = ________, size = "pop", title = "2007") +

Output Solution

Code Solution

ggplot(data, aes(x = gdpPercap_2007, y = lifeExp_2007, size = pop_2007)) +
  geom_smooth() +
  geom_point() +
  labs(x = "gdpPercap", y = "lifeExp", size = "pop", title = "2007") +
  theme_classic()

Publication Quality Bubble Chart Fill-in Challenge

Fill in the missing pieces of the following code to generate a publication quality bubble chart.

ggplot(data, aes(________)) +
  geom_smooth(method = ________, color = "black", size = 2) +
  geom_point() +
  scale_size(range = c(________)) +
  scale_x_log10() +
  labs(x = "GDP/capita [adjusted US$]", y = "Life Expectancy [years]", 
       size = "Population [millions]", title = "2007") +
  theme_classic(________) +
  theme(axis.title = ________)

Output Solution

Code Solution

ggplot(data, aes(x = gdpPercap_2007, y = lifeExp_2007, 
                 size = pop_2007/1000000)) +
  geom_smooth(method = "lm", color = "black", size = 2) +
  geom_point() +
  scale_size(range = c(2, 20)) +
  scale_x_log10() +
  labs(x = "GDP/capita [adjusted US$]", y = "Life Expectancy [years]", 
       size = "Population [millions]", title = "2007") +
  theme_classic(base_size = 24, base_family = "Helvetica") +
  theme(axis.title = element_text(size = 36))

Key Points

• Bubble charts represent a relationship with three variables

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