Ggplot2 legend with actual values instead of log

Question

I created a map using ggplot2 where I show the trade balance of European countries vis-a-vis the rest of the world, using the code below:

library(ggplot2)
library(sf)
library(giscoR)

data <- read.csv("~/Downloads/full202052 (1)/full202052.dat")

data2 = data[data$TRADE_TYPE=="E",]

x = aggregate(VALUE_IN_EUROS ~ FLOW + PARTNER_ISO, data2, sum)

x = sapply(split(x, x$PARTNER_ISO), function(x) diff(x$VALUE_IN_EUROS))

x  = data.frame(Code = names(unlist(x)), Value = unlist(x))


eu = levels(as.factor(data$DECLARANT_ISO))

eu = gisco_get_countries(epsg = "4326", year = "2020", resolution = "3", country = c(eu[!eu %in% c("GB","GR")], "UK", "EL"))

borders <- gisco_get_countries(epsg = "4326", year = "2020", resolution = "3", country = x$Code)

merged <- merge(borders, x, by.x = "CNTR_ID", by.y = "Code", all.x = TRUE)

Africa <- gisco_get_countries(epsg = "4326", year = "2020", resolution = "3", region = "Africa")

ggplot(merged) +
geom_sf(aes(fill = sign(Value/1000000000)*log(abs(Value/1000000000))), color = NA, alpha = 0.9) +
#geom_sf(aes(fill = Value/1000000000), color = NA, alpha = 0.9) +
geom_sf(data = eu, fill = "deepskyblue4", color = NA, size = 0.1) +
geom_sf(data = Africa, fill = NA, size = 0.1, col = "grey30") +
geom_sf(data = borders, fill = NA, size = 0.1, col = "grey30") +
scale_fill_gradient2(
name = "Euros (Billions)",
guide = guide_legend(
  direction = "horizontal",
  keyheight = 0.5,
  keywidth = 2,
  title.position = "top",
  title.hjust = 0,
  label.hjust = .5,
  nrow = 1,
  byrow = TRUE,
  reverse = FALSE,
  label.position = "bottom"
)
) + theme_void()+
labs(
title = "Trade Balance of Europe Vis-à-vis the World (2020)",
subtitle = "(In Billions of Euros)",
caption = paste0("Source: Eurostat")) +
# Theme
theme(
#plot.background = element_rect(fill = "black"),
plot.title = element_text(
  color = "black",
  hjust = 0.5,
  vjust = -1,
),
plot.subtitle = element_text(
  color = "black",
  hjust = 0.5,
  vjust = -2,
  face = "bold"
),
plot.caption = element_text(
  color = "black",
  size = 6,
  hjust = 0.5,
  margin = margin(b = 2, t = 13)
),
legend.text = element_text(
  size = 7,
  color = "black"
),
legend.title = element_text(
  size = 7,
  color = "black"
),
legend.position = c(0.5, 0.02),
)

And it results in the following map:

The legend of the map show -5, 0, 5, but I want it to show -200, 0, 200 instead. Can anyone please give me a clue as to how to change the legend labels to the numbers I want? Thanks.

score 1 · Answer 1 · answered Jan 26 '22 at 09:51

This problem is independent of sf. Instead of transforming the data in the aes statement you can use the trans argument of the color or fill scale. More different transformations can be found in the scales package. If needed you can also find instructions for creating new ones there. This is an example of using the trans argument:

library(ggplot2)

df<-data.frame(x=-4:4, y=-4:4, col=exp(-4:4))

ggplot(df) +
  geom_point(aes(x=x,y=y,color= sign(col)*log(abs(col))))

ggplot(df) +
  geom_point(aes(x=x,y=y,color= col))+
  scale_color_continuous(trans='log')

Thank you for your useful answer, I used the `trans = pseudolog10_trans` from the `ggallin` instead, and it gave exactly the results I wanted. — Saïd Maanan, Jan 27 '22 at 16:48

score 0 · Accepted Answer · answered Jan 27 '22 at 16:46

I fixed the problem using the ggallin package and the pseudolog10_trans function. The updated code is as follows:

ggplot(merged) +
geom_sf(aes(fill = Value/1000000000), color = NA, alpha = 0.9, size = 0.1) +
geom_sf(data = eu, fill = "deepskyblue4", color = NA, size = 0.1) +
#geom_sf(data = Africa, fill = NA, size = 0.1, col = "grey30") +
#geom_sf(data = borders, fill = NA, size = 0.1, col = "grey30") +
scale_fill_gradient2(
trans = pseudolog10_trans,
name = "Euros (Billions)",
guide = guide_legend(
  direction = "horizontal",
  keyheight = 0.5,
  keywidth = 2,
  title.position = "top",
  title.hjust = 0,
  label.hjust = .5,
  nrow = 1,
  byrow = TRUE,
  reverse = FALSE,
  label.position = "bottom"
 )
 ) + theme_void()+
 labs(
title = "Trade Balance of Europe Vis-à-vis the World (2020)",
subtitle = "(In Billions of Euros)",
caption = paste0("Source: Eurostat")) +
# Theme
theme(
#plot.background = element_rect(fill = "black"),
plot.title = element_text(
  color = "black",
  hjust = 0.5,
  vjust = -1,
),
plot.subtitle = element_text(
  color = "black",
  hjust = 0.5,
  vjust = -2,
  face = "bold"
),
plot.caption = element_text(
  color = "black",
  size = 6,
  hjust = 0.5,
  margin = margin(b = 2, t = 13)
),
legend.text = element_text(
  size = 7,
  color = "black"
),
legend.title = element_text(
  size = 7,
  color = "black"
),
legend.position = c(0.5, 0.02),

)

And it resulted in the following map:

Ggplot2 legend with actual values instead of log

2 Answers2