Hex country density

gistfile1.txt

library(ggplot2)
library(units)
library(sf)

world <- rnaturalearth::ne_countries(returnclass = "sf", scale = 10) |> 
  st_transform(crs = "+proj=moll")


# Make a hexagonal grid
size <- 1000000
units(size) <- as_units("km^2")
grid <- st_make_grid(world, cellsize = size, square = FALSE) 

# Remove hexagons that fall outside the world 
outside <- grid |> 
  st_centroid() |> 
  st_transform(crs = "+proj=lonlat") |> 
  st_is_empty()
grid <- grid[!outside]

# Compute number of countries tha fall within each hex  
n_country <- st_intersects(grid, world) |> 
  lengths()

# Sort in ascending order so darker hex get drawn last. 
# Otherwise the perimeter of dark hexes gets obscured by 
# the perimeter of lighter hexes. 
o <- order(n_country)
grid <- grid[o]
n_country <- n_country[o]

ggplot() +
  geom_sf(data = grid,
          aes(fill = cut_width(n_country, 1, boundary = 0),
              color = after_scale(colorspace::darken(fill, 0.2))),
          linewidth = 0.5) +
  geom_sf(data = world, fill = NA, linewidth = 0.1, color = alpha("black", .3)) +
  scale_fill_continuous(name = NULL, super = metR::ScaleDiscretised, 
                        low = "white", high = "#de3e80",
                       guide = guide_colorsteps(barwidth = 20, 
                                                barheight = 0.4, 
                                                show.limits = TRUE, frame.colour = "black")) +
  theme_void(base_size = 16) +
  theme(legend.position = "bottom") +
  labs(title = "Countries per 1 million squared kilometre")