Overview

Teaching: 5 min
Exercises: 15 min

Questions

• What kind of scientific question does a stacked area chart address?

• How do I generate a stacked area chart with ggplot2?

Objectives

• To generate a stacked area chart using ggplot2

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

• “How has the composition of the world population among continents changed from 1952-2007?”
• Composition changing over time
• Stacked area chart

Implement faceted table of histograms.

• geom_line(), geom_area()
• guide_legend()

Chart Improvement Challenge

Here is a incomplete (or bad) example of the chart we are going for. Modify the code to a publication quality stacked area chart.

total_pop_continent<- pop_by_continent %>%
  group_by(continent, year) %>%
  summarize(tot_pop = sum(population)/1000000000)

ggplot(total_pop_continent, aes(as.numeric(year), tot_pop, 
       group = continent)) +
  geom_line(position = "stack")

Output Solution

Code Solution

ggplot(total_pop_continent, aes(as.numeric(year), tot_pop, 
       fill = continent)) + 
  geom_area() +
  labs(x = "Year", y = "Population [billions]", 
       fill = "Continent") +
  theme_classic(base_size = 24, base_family = "Helvetica") +
  theme(axis.title = element_text(size = 36))

Key Points

• Stacked area charts represent a composition changing over time.

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