In sgplot: Graphic Styles and Colours for Scottish Government Plots

Annotations

Labelling your chart is often preferable to using a legend, as often this relies on a user matching the legend to the data using colour alone. The legend can be removed from a chart by setting legend = "none" in theme_sg().

The easiest way to add an annotation is to manually define the co-ordinates of the required position.

ann_data <- gapminder |>
  filter(country %in% c("United Kingdom", "China"))

#| fig.alt = "A multiple line chart with colour co-ordinated line labels using sgplot theme and main palette."

ann_data |>
  ggplot(aes(x = year, y = lifeExp, colour = country)) +
  geom_line(linewidth = 1) +
  theme_sg(legend = "none") +
  scale_colour_discrete_sg() +
  scale_y_continuous(limits = c(0, 82),
                     breaks = seq(0, 80, 20),
                     expand = c(0, 0)) +
  scale_x_continuous(limits = c(1952, 2017),
                     breaks = seq(1952, 2017, 5)) +
  annotate(geom = "label", x = 2008, y = 73, label = "China",
           colour = sg_colour_values[1],
           label.size = NA,
           hjust = 0, vjust = 0.5) +
  annotate(geom = "label", x = 2008, y = 79.4, label = "United Kingdom",
           colour = sg_colour_values[2],
           label.size = NA,
           hjust = 0, vjust = 0.5) +
  labs(
    x = "Year",
    y = NULL,
    title = "Living Longer",
    subtitle = "Life Expectancy in the United Kingdom and China 1952-2007",
    caption = "Source: Gapminder"
  )

However, this makes the code difficult to reuse as values are hard coded and not automatically generated from the data. Automating the position of annotations is possible, but more fiddly.

The following examples use geom_label() to use values from the data to position annotations. geom_label() draws a rectangle behind the text (white by default) and a border the same colour as the text (label_size = NA can be used to remove the border). geom_text() is also an option for annotations, but this does not include a background and so can be harder for text to read if it overlaps with other chart elements. These functions also have nudge arguments that can be used to displace text to improve the positioning.

Note that in the previous examples, annotate() also requires a geom (label or text). These operate in the same way as geom_label() and geom_text(), but as discussed, annotate() is only able to deal with fixed values.

#| fig.alt = "A multiple line chart with colour co-ordinated line labels using sgplot theme and main2 palette."

ann_labs <- ann_data |>
  group_by(country) |>
  mutate(min_year = min(year)) |>
  filter(year == max(year)) |>
  ungroup()

ann_data |>
  ggplot(aes(x = year, y = lifeExp, colour = country)) +
  geom_line(linewidth = 1) +
  theme_sg(legend = "none") +
  scale_colour_discrete_sg() +
  scale_y_continuous(limits = c(0, 82),
                     breaks = seq(0, 80, 20),
                     expand = c(0, 0)) +
  scale_x_continuous(limits = c(1952, 2017),
                     breaks = seq(1952, 2017, 5)) +
  geom_label(data = ann_labs,
             aes(x = year, y = lifeExp, label = country, colour = country),
             hjust = 0,
             vjust = 0.5,
             nudge_x = 0.5,
             label.size = NA) +
  labs(
    x = "Year",
    y = NULL,
    title = "Living Longer",
    subtitle = "Life Expectancy in the United Kingdom and China 1952-2007",
    caption = "Source: Gapminder"
  )

Annotations may also be used to add value labels to a bar chart. Note that geom_text() is used here as a background is not required.

#| fig.alt = "A bar chart with white text labels at the end of each bar."

ggplot(bar_data, aes(x = reorder(country, -lifeExp), y = lifeExp)) +
  geom_col(fill = sg_colour_values["dark-blue"]) +
  geom_text(aes(label = round(lifeExp, 1)),
            nudge_y = -5, colour = "white") +
  theme_sg() +
  scale_y_continuous(expand = c(0, 0)) +
  labs(
    x = NULL,
    y = NULL,
    title = "Iceland has the highest life expectancy in Europe",
    subtitle = "Life expectancy in European countries, 2007",
    caption = "Source: Gapminder"
  )

Note: The annotate() function should be used to add annotations with manually defined positioning co-ordinates, whereas geom_label() and geom_text() should be used when using co-ordinates defined in a data frame. Although the reverse may work, text can appear blurry.