How to (automatically) add custom icon to a treemap using ggplot2 and treemapify?

I'm trying to illustrate land cover data by the means of a treemap. I managed to create a simple treemap and to "grab" some icons. Unfortunately, I struggle to include these icons into the treemap which would help to illustrate the type of land cover.

This is an example code:

# create dataframe
df <- data.frame(category = c("forest", "greenland", "crops"),
                 area = c(20, 10, 70)
)
df$label = paste0(df$area,"%")

# load icons
library(magick)
icon_crops2 <- image_read("https://upload.wikimedia.org/wikipedia/commons/thumb/7/79/Agriculture_-_The_Noun_Project.svg/512px-Agriculture_-_The_Noun_Project.svg.png")
icon_forest2 <- image_read("https://upload.wikimedia.org/wikipedia/commons/thumb/d/da/BSicon_FOREST.svg/500px-BSicon_FOREST.svg.png")
icon_greenland2 <- image_read("https://upload.wikimedia.org/wikipedia/commons/thumb/2/2b/Wikidata_Morse_code_logo_grassroots.svg/600px-Wikidata_Morse_code_logo_grassroots.svg.png")

# add icons to dataframe
df$icons = c(icon_crops2, icon_forest2, icon_greenland2)
print(df$icons)

# plot treemap without icons
library(ggplot2)
library(treemapify)

ggplot(df, aes(area = area, 
                     fill = category, 
                     label = paste(category,label,sep="\n"),
                     subgroup = category)) +
  geom_treemap() +
  geom_treemap_text(colour = "black", place = "center") +
  theme(legend.position = "none")

This results in the following image:

Yet, I would like to have something like this (created with GIMP):

Although I could insert the icons manually, e.g. by using GIMP, I'm looking for an automatic way.

Anyone has an idea how to do this?

Solution

One option would be to use ggimage::geom_image. To place the images we could use treemapify::treemapify() to create a dataset with the coordinates of the rectangles which could then be passed to geom_image to place the images in the right rectangles:

# create dataframe
df <- data.frame(
  category = c("forest", "greenland", "crops"),
  area = c(20, 10, 70)
)
df$label <- paste0(df$area, "%")

# plot treemap without icons
library(ggplot2)
library(treemapify)
library(ggimage)

dat_image <- treemapify(df,
  area = "area",
  layout = "squarified",
  start = "bottomleft"
) |>
  transform(x = .5 * (xmin + xmax), y = .5 * (ymin + ymax))

dat_image$icons <- c(
  "https://upload.wikimedia.org/wikipedia/commons/thumb/7/79/Agriculture_-_The_Noun_Project.svg/512px-Agriculture_-_The_Noun_Project.svg.png",
  "https://upload.wikimedia.org/wikipedia/commons/thumb/d/da/BSicon_FOREST.svg/500px-BSicon_FOREST.svg.png",
  "https://upload.wikimedia.org/wikipedia/commons/thumb/2/2b/Wikidata_Morse_code_logo_grassroots.svg/600px-Wikidata_Morse_code_logo_grassroots.svg.png"
)

ggplot(df, aes(
  area = area,
  fill = category,
  label = label,
  subgroup = category
)) +
  geom_treemap() +
  geom_treemap_text(colour = "black", place = "center") +
  scale_x_continuous(limits = c(0, 1), expand = c(0, 0)) +
  scale_y_continuous(limits = c(0, 1), expand = c(0, 0)) +
  geom_image(data = dat_image, aes(x = x, y = y, image = icons), inherit.aes = FALSE, nudge_y = .1, size = .1) +
  theme(
    legend.position = "none",
    axis.line = element_blank(),
    axis.text = element_blank(),
    axis.title = element_blank(),
    axis.ticks = element_blank()
  )