Inaccessibility

IMG_9811 – CC-BY-NC by Eddie Lawrance

Day 7 of 30DayMapChallenge: « Accessibility » (previously).

Well, let us be rebellious and instead seek inaccessibility; more precisely the pole of inaccessibility of France (the Hexagon): the farthest location from the boundary. Not to be confused with the centroid.

library(sf)
library(dplyr)
library(ggplot2)
library(glue)
library(purrr)
library(polylabelr)

Data

We’ll use again the french administrative units (get the data from this post).

# France boundary
fr <- read_sf("~/data/adminexpress/adminexpress_cog_simpl_000_2022.gpkg",
              layer = "region") |>
  filter(insee_reg > "06",
         insee_reg != "94") |> 
  st_transform("EPSG:2154") |> 
  st_union()

# French communes to get the point name
com <- read_sf("~/data/adminexpress/adminexpress_cog_simpl_000_2022.gpkg",
               layer = "commune") |>
  filter(insee_reg > "06",
         insee_reg != "94") |> 
  st_transform("EPSG:2154")

Compute the POI

Get the inaccessibility pole of France with {polylabelr} and intersects with the commune layer to find the nearest city.

fr_poi <- poi(fr) |> 
  pluck(1) |> 
  as_tibble() |> 
  st_as_sf(coords = c("x", "y"), crs = "EPSG:2154") |> 
  st_join(com)

fr_poi_circle <- fr_poi |> 
  mutate(geometry = st_buffer(geometry, dist))

fr_centroid <- fr |> 
  st_centroid()

It seems to be in Saint-Palais in the Cher département.

Map

fr_poi |> 
  ggplot() +
  geom_sf(data = fr) +
  geom_sf(data = fr_poi_circle, linewidth = 1, linetype = 3) +
  geom_sf(data = fr_centroid, color = "darkgrey") +
  geom_sf() +
  geom_sf_text(aes(label = nom), vjust = -.5) +
  labs(title = "Pole of inaccessibility",
       subtitle = "France",
       x = "", y = "",
       caption = glue("https://r.iresmi.net/ - {Sys.Date()}
                      data from IGN Adminexpress 2022")) +
  theme_minimal() +
  theme(plot.caption = element_text(size = 6, 
                                    color = "darkgrey"))

Figure 1: Inaccessibility pole of France (black). The grey dot is the centroid