I have been lucky to fly to a few countries around the world. Like any other bored traveller, I thumb through the airline magazines and look at the air travel route maps. These maps are beautifully stylised depictions of the world with gently curved lines between the many destinations. I always wanted such a map for my own travel adventures.
Create Air Travel Route Maps using ggplot2
The first step was to create a list of all the places I have flown between at least once. Paging through my travel photos and diaries, I managed to create a pretty complete list. The structure of this document is simply a list of all routes (From, To) and every flight only gets counted once. The next step finds the spatial coordinates for each airport by searching Google Maps using the geocode function from the ggmap package. In some instances, I had to add the country name to avoid confusion between places.
# Read flight list flights <- read.csv("flights.csv", stringsAsFactors = FALSE) # Lookup coordinates library(ggmap) airports <- unique(c(flights$From, flights$To)) coords <- geocode(airports) airports <- data.frame(airport=airports, coords)
We now we have a data frame of airports with their coordinates and can create air travel route maps. The data frames are merged so that we can create air travel route maps using the curve geom. The borders function of ggplot2 creates the map data. The ggrepel package helps to prevent overplotting of text.
# Add coordinates to flight list flights <- merge(flights, airports, by.x="To", by.y="airport") flights <- merge(flights, airports, by.x="From", by.y="airport") # Plot flight routes library(ggplot2) library(ggrepel) worldmap <- borders("world", colour="#efede1", fill="#efede1") # create a layer of borders ggplot() + worldmap + geom_curve(data=flights, aes(x = lon.x, y = lat.x, xend = lon.y, yend = lat.y), col = "#b29e7d", size = 1, curvature = .2) + geom_point(data=airports, aes(x = lon, y = lat), col = "#970027") + geom_text_repel(data=airports, aes(x = lon, y = lat, label = airport), col = "black", size = 2, segment.color = NA) + theme(panel.background = element_rect(fill="white"), axis.line = element_blank(), axis.text.x = element_blank(), axis.text.y = element_blank(), axis.ticks = element_blank(), axis.title.x = element_blank(), axis.title.y = element_blank() )
I also tried to use ggmap package to display the maps to get a satellite image background. This did not work because the curve geom struggles with the map projection methods used in ggmap. Another problem is that the flight from Auckland to Los Angeles is drawn the wrong way. I hope no flat-earthers will see this map because they might use it as prove that the world is flat.
Another way of visualising this type of data is using a network diagram provided by the igraph package. This visualisation shows the logic between the locations and not their spatial locations.
# Network visualisation library(igraph) edgelist <- as.matrix(flights[c("From", "To")]) g <- graph_from_edgelist(edgelist, directed = TRUE) g <- simplify(g) par(mar=rep(0,4)) plot.igraph(g, edge.arrow.size=0, edge.color="black", edge.curved=TRUE, edge.width=2, vertex.size=3, vertex.color=NA, vertex.frame.color=NA, vertex.label=V(g)$name, vertex.label.cex=3, layout=layout.fruchterman.reingold )
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