Recently, I was asked whether I could create an international trade network with flags as nodes. Therefore, I thought I would write a post introducing the ggflags packages and how to use it in network visualisation.

I am creating this visualisation in R, and relying on a number of packages:

ITNr for the international trade network data that we use in the example. However, you the visualisation steps I will outline can be applied to any country level network (that is a set of countries connect by any links - this could be trade, investment etc.)
ggflags to visualise the nodes as flags. This package is available on GitHub (currently not on CRAN)
ggnetwork is used to plot the network
countrycode and magrittr to process node names into the correct form to be used by ggflags
I also use igraph and intergraph as the example network from ITNr is a igraph object

Update: An example of a published article using these flag network visualisations can be found here

Load, clean and process network data

First we load the example data from the ITNr, an example International Trade Network (ITN). We also calculate network centrality metrics, as these can be used later in the visualisation - such as setting node size based on centrality.

library(ITNr)

data("ELEnet16")

## Centrality Measures
ITNcent<-ITNcentrality(ELEnet16)

## Add these as attributes to the igraph object
library(igraph)
V(ELEnet16)$cent<-ITNcent$Weighted.Out.Degree
V(ELEnet16)$centALL<-ITNcent$Weighted.Degree.All

We then need to convert this into an object compatible with ggnetwork so that we can take advantage of the ggflagsfunctionality.

library(ggnetwork)
library(intergraph)

## Convert igraph object to network object
ITNnet<-asNetwork(ELEnet16)

##Convert this to ggnetwork dataframe
ITN<-ggnetwork(ITNnet)

Before we can visualise this data, we need to do some additional cleaning, such as making use the ggflags package can recognise the country names. ggflags needs the country names to be in lowercase and in the form of 2 digit ISO codes - here is where the countrycodes packages is very useful.

library(countrycode)
# Create new column called country
# Need to make sure the vertex names are characters,
# as ggnetwork may have converted them to factors.

ITN$country<-countrycode(as.character(ITN$vertex.names),
                         "iso3c","iso2c")

# In this example - the vertex anmes are 3 digit ISO codes
# However, countrycode has a wide range of function to 
# convert country names to 2 sigit iso codes

# We then need to make the codes lowercase
library(magrittr)
ITN$country%<>%tolower()

Network Visualisation

THe data is now in a form, where we can plot the network and make use of the ggflags package. In this example node size is based on weighted out degree centrality and tie size is based on the level of trade in the network (the edge weight in the igraph object)

#First install ggflags
devtools::install_github("rensa/ggflags")
library(ggflags)
# I would recommend opening a tiff file, so that you get a higher quality visualisation
tiff('Example.tiff', units="in", width=6, height=5, res=300)

ggplot(ITN, aes(x = x, y = y, xend = xend, yend = yend,
                country=country,size=cent)) +
  geom_edges(size = E(ELEnet16)$weight*.5,#the edge weight from the igraph object
             color="grey") +
  geom_flag() + 
  scale_size(range = c(2, 13))+ #Node size scale
  guides(colour=FALSE,size=FALSE)+ #Remove the legends
  theme_blank()

dev.off()

## Warning: Using `size` aesthetic for lines was deprecated in ggplot2 3.4.0.
## ℹ Please use `linewidth` instead.
## This warning is displayed once every 8 hours.
## Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
## generated.

## Warning: The `<scale>` argument of `guides()` cannot be `FALSE`. Use "none" instead as
## of ggplot2 3.3.4.
## This warning is displayed once every 8 hours.
## Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
## generated.

R Country Networks Visualisation