how to add IPCC stippling to global map with ggplot2

Question

I need to add IPCC(-style) stippling to a global map as in this post. However I would like to use one of the functions of ggplot2 for doing so.

Here an example of data and plot:

test.csv

df=read.csv("/home/my_folder/test.csv")

library(ggplot2)
library(metR)

plot_df = ggplot() +
  geom_contour_fill(data=df, aes(x=V1, y=V2, z = value)) +
  scale_fill_steps2(name = "", low = "#0571b0", mid = '#ffffbf', high = '#ca0020')

print(plot_df)

How can I add IPCC stippling to this image?

I tried using geom_point() but the stippling are too large and mask the background colors.

Thanks

Edit

Following @Allan answer I am indeed able to add stippling as follows:

library(ggplot2)
library(ggpattern)

df=read.csv("~/...../test.csv")

df_stippl=df[c(10:47, 100:250, 500:510, 707:1000, 1508:1699, 2500:2600, 2680:2690, 3400:4300),]

plot_df = ggplot() +
  
  geom_contour_fill(data=df, aes(x=V1, y=V2, z = value)) +
  
  stat_contour_fill(data=df_stippl, aes(x=V1, y=V2, z = value), geom = "polygon_pattern", 
                    pattern_fill = "black", pattern_size = 0,
                    pattern = "crosshatch", pattern_spacing = 0.02,
                    pattern_angle = 45, pattern_density = 0.1) +
  
  scale_fill_steps2(name = "", low = "#0571b0", mid = '#ffffbf', high = '#ca0020')

print(plot_df)

However, when I save the figure in pdf:

pdf('~/...../figure.pdf', width = 10, height = 6.6)
print(plot_df)
dev.off()

I get full stippling all over the globe and not only in the areas of df_stippl.

Answer 1

You could do this a couple of ways. Perhaps the easiest is to get the centre points of a hexagonal grid covering your data and draw with geom_point

library(ggplot2)
library(metR)
library(hexbin)

df = read.csv("../test.csv")

hb  <- erode(hexbin(df$V1, df$V2, xbins = 55))
df2 <- as.data.frame(hcell2xy(hb))

ggplot() +
  geom_contour_fill(data=df, aes(x=V1, y=V2, z = value)) +
  scale_fill_steps2(name = "", low = "#0571b0",
                    mid = '#ffffbf', high = '#ca0020') +
  geom_point(data = df2, aes(x, y), color = "black", size = 1) +
  theme_bw() 

If you want the dots to have a different density, you can change xbins

hb  <- erode(hexbin(df$V1, df$V2, xbins = 20))
df2 <- as.data.frame(hcell2xy(hb))

ggplot() +
  geom_contour_fill(data=df, aes(x=V1, y=V2, z = value)) +
  scale_fill_steps2(name = "", low = "#0571b0",
                    mid = '#ffffbf', high = '#ca0020') +
  geom_point(data = df2, aes(x, y), color = "black", size = 1) +
  theme_bw() 

An alternative is to filter out some of the rows of your data frame and plot the points there:

ggplot(df, aes(V1, V2)) +
  geom_contour_fill(aes(z = value)) +
  geom_point(data = df[(df$V1 + df$V2) %% 3 == 0,], color = "black", size = 1) +
  scale_fill_steps2(name = "", low = "#0571b0", 
                    mid = '#ffffbf', high = '#ca0020') +
  theme_bw() 

Compare all of these to just plotting the points:

ggplot(df, aes(V1, V2)) +
  geom_contour_fill(aes(z = value)) +
  geom_point(color = "black", size = 1) +
  scale_fill_steps2(name = "", low = "#0571b0", 
                    mid = '#ffffbf', high = '#ca0020') +
  theme_bw() 

---

Edit

If you want cross-hatching you can do:

library(ggplot2)
library(metR)
library(ggpattern)

df <- read.csv("../test.csv")

ggplot(df, aes(V1, V2)) +
  stat_contour_fill(aes(z = value), geom = "polygon_pattern", 
                      pattern_fill = "black", pattern_size = 0,
                      pattern = "crosshatch", pattern_spacing = 0.02,
                      pattern_angle = 45, pattern_density = 0.1) +
  scale_fill_steps2(name = "", low = "#0571b0", mid = '#ffffbf',
                    high = '#ca0020') +
  theme_bw() 

To save your plot as pdf, you will need to use cairo_pdf:

df_stippl=df[c(10:47, 100:250, 500:510, 707:1000, 1508:1699, 
               2500:2600, 2680:2690, 3400:4300),]

plot_df = ggplot() +
  geom_contour_fill(data=df, aes(x=V1, y=V2, z = value)) +
  stat_contour_fill(data=df_stippl, aes(x=V1, y=V2, z = value), 
                    geom = "polygon_pattern", 
                    pattern_fill = "black", pattern_size = 0,
                    pattern = "crosshatch", pattern_spacing = 0.02,
                    pattern_angle = 45, pattern_density = 0.1) +
  scale_fill_steps2(name = "", low = "#0571b0", mid = '#ffffbf', 
                    high = '#ca0020')

cairo_pdf('../figure.pdf', width = 10, height = 6.6)
print(plot_df)
dev.off()

figure.pdf