Give an example how and why to use line borders instead of polygons outlines in maps -- https://ikashnitsky.github.io/2023/map-borders

explain-map-borders.R

#===============================================================================
# 2020-04-08 -- twitter upd 2023-01-01 ik-q
# Showcase the map hack -- use border lines instead of polygon outlines
# https://twitter.com/ikashnitsky/status/1247875600305598464
# https://ikashnitsky.github.io/2023/map-borders
# Ilya Kashnitsky, ilya.kashnitsky@gmail.com
#===============================================================================

library(tidyverse)
library(sf)

set.seed(911)

# subset Greence, NUTS-3 regions
library(eurostat)
greece <- eurostat_geodata_60_2016 %>% 
    filter(LEVL_CODE==3,
           str_sub(geo, 1, 2) == "EL") %>% 
    # create random values for filling the ploygons
    mutate(random = runif(length(id))) %>% 
    select(id, geometry, random) %>% 
    st_transform(crs = 3035)

# plot with polygon outlines
greece %>% 
    ggplot()+
    geom_sf(aes(fill = random), color = 2, size = 1)+
    labs(title = "Polygons outlined")+
    scale_fill_viridis_c(begin = .5)+
    theme_map()+
    theme(plot.background = element_rect(color = NA, fill = "#eeffff"))

gg_outline <- last_plot()

# produce border lines with rmapshaper::ms_innerlines()
library(rmapshaper)
bord <- greece %>% ms_innerlines()

# now plot without polygon outlines and with borders as lines
greece %>% 
    ggplot()+
    geom_sf(aes(fill = random), color = NA)+
    geom_sf(data = bord, color = 2, size = 1)+
    labs(title = "Borders as lines")+
    scale_fill_viridis_c(begin = .5)+
    theme_map()+
    theme(plot.background = element_rect(color = NA, fill = "#eeffff"))

gg_bord <- last_plot()

# put side by side
library(patchwork)
(
    gg_outline + gg_bord 
)  + 
    plot_layout(guides = "collect")+
    plot_annotation(
        caption = "! Look at the islands", 
        theme = theme(plot.background = element_rect(color = NA, fill = "#eeffff"))
    )

ggsave("out.png", width = 6, height = 3)