streamgraph

R code of the ggplot2 example

library(ggplot2)
library(dplyr)
library(gapminder)

## Stacked areas centred on zero: each year's stack is shifted down by half its total.
streams <- gapminder |>
  group_by(year, continent) |>
  summarise(pop = sum(as.numeric(pop)) / 1e9, .groups = "drop") |>
  group_by(year) |>
  arrange(desc(continent), .by_group = TRUE) |>
  mutate(top = cumsum(pop) - sum(pop) / 2, bottom = top - pop) |>
  ungroup()
names_at <- streams |>
  filter(year == 2007) |>
  mutate(y = (top + bottom) / 2,
         ## Oceania's thin stream: its name moved below Europe's.
         y = ifelse(continent == "Oceania", y - 0.15, y))

p <- ggplot(streams, aes(x = year, ymin = bottom, ymax = top, fill = continent)) +
  geom_ribbon(colour = "white", linewidth = 0.2) +
  geom_text(data = names_at, aes(x = 2008, y = y, label = continent, colour = continent),
            hjust = 0, size = 3, inherit.aes = FALSE) +
  scale_fill_manual(values = continent_colors) +
  scale_colour_manual(values = continent_text_colors) +
  scale_x_continuous(breaks = seq(1952, 2002, by = 10), expand = expansion(add = c(0.5, 12))) +
  scale_y_continuous(labels = \(x) lex_number(abs(x))) +
  labs(title = "Africa's population overtook Europe's in the 1980s",
       subtitle = "Population of the 142 Gapminder countries, by continent",
       x = NULL, y = "Population (billions)",
       caption = "Data: Gapminder, via the gapminder R package") +
  theme_lex_viz(grid = "x", arrows = "") +
  theme(legend.position = "none")