GeoJSON Version of CBC Quebec Ridings Hex Cartograms with Example Usage in R

October 10, 2018
By

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

The CBC covered the recent (as of the original post-time on this blog entry) Quebec elections and used a well-crafted hex grid map to display results:

They have a great ‘splainer on why they use this type of map.

Thinking that it may be useful for others, I used a browser Developer Tools inspector to yank out the javascript-created SVG and wrangled out the hexes using svg2geojson🔗 and put them into a GeoJSON file along with some metadata that I extracted from the minified javascript from the CBC’s site and turned into a data frame using the V8🔗 package. Since most of the aforementioned work was mouse clicking and ~8 (disjointed) lines of accompanying super-basic R code, there’s not really much to show wrangling-wise1, but I can show an example of using the new GeoJSON file in R and the sf🔗 package:

library(sf)
library(ggplot2)

# get the GeoJSON file from: https://gitlab.com/hrbrmstr/quebec-hex-ridings or https://github.com/hrbrmstr/quebec-hex-ridings
sf::st_read("quebec-ridings.geojson", quiet = TRUE, stringsAsFactors = FALSE) %>% 
  ggplot() +
  geom_sf(aes(fill = regionname)) +
  coord_sf(datum = NA) +
  ggthemes::scale_fill_tableau(name = NULL, "Tableau 20") +
  ggthemes::theme_map() +
  theme(legend.position = "bottom")

And, with a little more ggplot2-tweaking and some magick, we can even put it in the CBC-styled border:

library(sf)
library(magick)
library(ggplot2)

plt <- image_graph(1488, 1191, bg = "white")
sf::st_read("quebec-ridings.geojson", quiet=TRUE, stringsAsFactors=FALSE) %>% 
  ggplot() +
  geom_sf(aes(fill=regionname)) +
  coord_sf(datum=NA) +
  scale_x_continuous(expand=c(0,2)) +
  scale_y_continuous(expand=c(0,0)) +
  ggthemes::theme_map() +
  theme(plot.margin = margin(t=150)) +
  theme(legend.position = "none")
dev.off()

# get this bkgrnd img from the repo
image_composite(plt, image_read("imgs/background.png")) %>% 
  image_write("imgs/composite-map.png")

You can tweak the border color with magick🔗 as needed and there’s a background2.png in the imgs directory in the repo that has the white inset that you can further composite as needed.

With a teensy bit of work you should be able adjust the stroke color via aes() to separate things as the CBC did.

FIN

It’s important to re-state that the CBC made the original polygons for the hexes (well, they made a set of grid points and open source software turned it into a set of SVG paths) and the background images. All I did was some extra bit of wrangling and conversionating2.

1 I can toss a screencast if there’s sufficient interest.
2 Totally not a word.

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