World Map Panel Plots with ggplot2 2.0 & ggalt

December 29, 2015
By

(This article was first published on R – rud.is, and kindly contributed to R-bloggers)

James Austin (@awhstin) made some #spiffy 4-panel maps with base R graphics but also posited he didn’t use ggplot2 because:

ggplot2 and maps currently do not support world maps at this point, which does not give us a great overall view.

That is certainly a box I would not put ggplot2 into, especially with the newly updated R maps (et al) packages, ggplot2 2.0 and my (still in development) ggalt package (though this was all possible before ggplot2 2.0 and ggalt). NOTE: I have no idea why I get so defensive about ggplot2 besides the fact that it’s one the best visualization tools ever created.

Here’s all you need to use the built-in facet options of ggplot2 to make the 4-panel plot (as James points out, you can get the data file from here: (CLIWOC15.csv)[http://www.austinwehrwein.com/wp-content/uploads/2015/12/CLIWOC15.csv]):

library(ggplot2)  # FYI you need v2.0
library(dplyr)    # yes, i could have not done this and just used 'subset' instead of 'filter'
library(ggalt)    # devtools::install_github("hrbrmstr/ggalt")
library(ggthemes) # theme_map and tableau colors
 
world <- map_data("world")
world <- world[world$region != "Antarctica",] # intercourse antarctica
 
dat <- read.csv("CLIWOC15.csv")        # having factors here by default isn't a bad thing
dat <- filter(dat, Nation != "Sweden") # I kinda feel bad for Sweden but 4 panels look better than 5 and it doesn't have much data
 
gg <- ggplot()
gg <- gg + geom_map(data=world, map=world,
                    aes(x=long, y=lat, map_id=region),
                    color="white", fill="#7f7f7f", size=0.05, alpha=1/4)
gg <- gg + geom_point(data=dat, 
                      aes(x=Lon3, y=Lat3, color=Nation), 
                      size=0.15, alpha=1/100)
gg <- gg + scale_color_tableau()
gg <- gg + coord_proj("+proj=wintri")
gg <- gg + facet_wrap(~Nation)
gg <- gg + theme_map()
gg <- gg + theme(strip.background=element_blank())
gg <- gg + theme(legend.position="none")
gg

facetmaps

You can use a separate shapefile if you want, but this is quite minimalist (a feature James suggests is desirable) and emphasizes the routes quite nicely IMO.

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