NA values ​in choropleth plot legend with ggplot2 in R

Question

In a choropleth graphic map with ggplot2, an element corresponding to the NA values ​​of the variable Cuantil Esfuerzo Social por habitante is automatically included in the legend

I have tried a few things:

1. Using na.translate = F in scale_fill_manual() hides both the "NA" item from the legend and the polygons corresponding to those values. So the map is incomplete.
2. Another option that I have used (as it appears in the code) is to define a color and a specific label (Sin datos) for the "NA" values ​​to give more meaning to the graph.

There would be two options to build the graph according to the needs:

1. Hide in the legend the label of the "NA" values. And add an annotation (annotate()) for the "NA" values, with a rectangle and text.
2. To be able to separate (adding a space) the legend with the quartile intervals and a different one only with the corresponding, key and label, to the "NA" values.

Data: https://www.dropbox.com/s/b39pp4qmbhns658/geosmunicipiosmu.R?dl=0

Code:

library(ggplot2)

geosmunicipiosmu <- dget("geosmunicipiosmu.R")

colors = c("#fee5d9","#fcae91","#fb6a4a","#de2d26")

mapaemu <- ggplot(geosmunicipiosmu) +
  
  geom_sf(
    aes(
      fill = `Cuantil Esfuerzo Social por habitante`
    ),
    #fill="white", 
    #fill=NA,
    color="#FFFFFF",
    size=0.5
  ) +
  
  coord_sf(
    xlim = c(-3.1, -0.5)
  ) +

 theme_void() +
  
 scale_fill_manual(
  values = c(colors,"#2c2c2c"), # Color adicional para los valores "NA"
  labels = c(
   paste("[1Q]\n", format(cuartilin[2], big.mark=".", decimal.mark=",", nsmall = 2, digits = 2), "€", sep=""),
   paste("(2Q]\n", format(cuartilin[3], big.mark=".", decimal.mark=",", nsmall = 2, digits = 2), "€", sep=""),
   paste("(3Q]\n", format(cuartilin[4], big.mark=".", decimal.mark=",", nsmall = 2, digits = 2), "€", sep=""),
   paste("(4Q]\n", format(cuartilin[5], big.mark=".", decimal.mark=",", nsmall = 2, digits = 2), "€", sep=""),
   "Sin\ndatos" # Etiqueta personalizada para valores "NA"
  ),
  guide = guide_legend(
   direction = "horizontal",
   nrow = 1,
   label.position = "top",
   label.hjust = 1,
   keyheight = 0.75
  )
 ) +
  
 labs(
  title = "Título",
  subtitle = "Subtítulo",
  fill = "" # Etiqueta para la Leyenda
 ) +
  
 theme(
  text = element_text(color = "#22211d"),
  plot.background = element_rect(fill = "#ffffff", color = NA),
  panel.background = element_rect(fill = "#ffffff", color = NA),
  legend.background = element_rect(fill = "#ffffff", color = NA),
  plot.caption.position = "plot",
  legend.position = "bottom",
  legend.text = element_text(size = 14)
 )

mapaemu

The map right now:

Answer 1

I would suggest another alternative option, that consists on plotting a base layer on the desired NA color and then combine it with a second colorized layer using the na.translate = F approach. By doing this, the plot would have all the polygons as the base layer and the legend would omit the NAs. See below your code with these small modifications.

library(ggplot2)

geosmunicipiosmu <- dget("geosmunicipiosmu.R")

# Create cuartilin. This was not on your code, so I figured it out <--------------
cuartilin <- quantile(geosmunicipiosmu$`Esfuerzo Social por Habitante`, na.rm = TRUE)
colors <- c("#fee5d9", "#fcae91", "#fb6a4a", "#de2d26")

mapaemu <- ggplot(geosmunicipiosmu) +
  # Add this line to create the base layer <--------------
  geom_sf(fill = "grey50", color = "#FFFFFF") +
  geom_sf(
    aes(
      fill = `Cuantil Esfuerzo Social por habitante`
    ),
    color = "#FFFFFF",
    size = 0.5
  ) +
  coord_sf(
    xlim = c(-3.1, -0.5)
  ) +
  theme_void() +
  scale_fill_manual(
    # Now remove NA from legend <--------------
    na.translate = FALSE,
    values = colors, # No NA color needed any more <--------------
    labels = c(
      paste("[1Q]\n", format(cuartilin[2], big.mark = ".", decimal.mark = ",", nsmall = 2, digits = 2), "€", sep = ""),
      paste("(2Q]\n", format(cuartilin[3], big.mark = ".", decimal.mark = ",", nsmall = 2, digits = 2), "€", sep = ""),
      paste("(3Q]\n", format(cuartilin[4], big.mark = ".", decimal.mark = ",", nsmall = 2, digits = 2), "€", sep = ""),
      paste("(4Q]\n", format(cuartilin[5], big.mark = ".", decimal.mark = ",", nsmall = 2, digits = 2), "€", sep = "")
    ), # No NA label needed any more <--------------
    guide = guide_legend(
      direction = "horizontal",
      nrow = 1,
      label.position = "top",
      label.hjust = 1,
      keyheight = 0.75
    )
  ) +
  labs(
    title = "Título",
    subtitle = "Subtítulo",
    fill = "" # Etiqueta para la Leyenda
  ) +
  theme(
    text = element_text(color = "#22211d"),
    plot.background = element_rect(fill = "#ffffff", color = NA),
    panel.background = element_rect(fill = "#ffffff", color = NA),
    legend.background = element_rect(fill = "#ffffff", color = NA),
    plot.caption.position = "plot",
    legend.position = "bottom",
    legend.text = element_text(size = 14)
  )

mapaemu