Question

I would like to use R to generate a very basic world map with a specific set of countries filled with a red colour to indicate that they are malaria endemic countries.

I have a list of these countries in a data frame but am struggling to overlay them on a world map.

I have tried using the wrld_simpl object and also the joinCountryData2Map method in the rworldmap package.

I would comment on this answer to prevent addition of a possibly redundant question but I do not have enough reputation at the moment, apologies for this.

https://stackoverflow.com/a/9102797/1470099

I am having difficulty understanding the arguments given to the plot() command – I wondered if there was just an easy way to tell R to plot all of the country NAMEs in my list on the wrld_simpl map instead of using grepl() etc. etc.

plot(wrld_simpl, 
     col = c(gray(.80), "red")[grepl("^U", wrld_simpl@data$NAME) + 1])

Answer 1

Using the rworldmap package, you could use the following:

library(rworldmap)

theCountries <- c("DEU", "COD", "BFA")
# These are the ISO3 names of the countries you'd like to plot in red

malDF <- data.frame(country = c("DEU", "COD", "BFA"),
  malaria = c(1, 1, 1))
# malDF is a data.frame with the ISO3 country names plus a variable to
# merge to the map data

malMap <- joinCountryData2Map(malDF, joinCode = "ISO3",
  nameJoinColumn = "country")
# This will join your malDF data.frame to the country map data

mapCountryData(malMap, nameColumnToPlot="malaria", catMethod = "categorical",
  missingCountryCol = gray(.8))
# And this will plot it, with the trick that the color palette's first
# color is red

EDIT: Add other colors and include picture

## Create multiple color codes, with Burkina Faso in its own group
malDF <- data.frame(country = c("DEU", "COD", "BFA"),
  malaria = c(1, 1, 2))

## Re-merge
malMap <- joinCountryData2Map(malDF, joinCode = "ISO3",
  nameJoinColumn = "country")

## Specify the colourPalette argument
mapCountryData(malMap, nameColumnToPlot="malaria", catMethod = "categorical",
  missingCountryCol = gray(.8), colourPalette = c("red", "blue"))