Creates a gif of the world in different map projections

map_projections.R

library(tidyverse)
library(sf)
library(giscoR)
library(gganimate)

# world, with Greenland and Congo (roughly equal in area) in red
world <- gisco_get_countries(resolution = "20") %>% 
   mutate(color = ifelse(CNTR_ID %in% c('GL', 'CD'), 'red', 'black')) %>% 
   group_by(color) %>% 
   summarise() %>% 
   st_cast("MULTIPOLYGON")

# see also: https://proj.org/operations/projections/index.html
projs <- list(
   "Mercator" = "+proj=merc",
   "WGS 84" = "+proj=longlat",
   "Robinson" = "+proj=robin",
   "Compact Miller" = "+proj=comill",
   "Eckert I" = "+proj=eck1",
   "Eckert II" = "+proj=eck2",
   "Eckert III" = "+proj=eck3",
   "Eckert IV" = "+proj=eck4",
   "Mollweide" = "+proj=moll",
   "Azimuth Equidistant" = "+proj=aeqd",
   "Lambert Equal Area" = "+proj=laea",
   "Adams World in a Square 2" = "+proj=adams_ws2",
   "Sinusoidal (Sanson-Flamsteed)" = "+proj=sinu",
   "Interrupted Goode Homolosine" = "+proj=igh"
)

dd <- map_dfr(projs, function(p) {
   
   d <- world %>% 
      st_transform(p)
   
   dd <- rbind(st_coordinates(d[d$color == 'red', ]) %>%
                      as_tibble() %>% 
                  mutate(color = 'red'),
               st_coordinates(d[d$color == 'black', ]) %>%
                                      as_tibble() %>% 
                  mutate(color = 'black'))
   
   res <- dd %>% 
      select(x = X, y = Y, everything()) %>% 
      mutate(id = paste0(L1, L2, L3)) %>% 
      mutate(x_orig = x, y_orig = y, projection = p,
             x = (x - min(x)) / (max(x) - min(x)),
             y = (y - min(y)) / (max(y) - min(y)))
   
   res
   }) %>% 
   mutate(projection = factor(projection, levels = unlist(projs)))

anim <- ggplot(dd, aes(x = x, 
                       y = y, 
                       group = id, 
                       fill = color)) + 
   geom_polygon(color = NA) +
   transition_states(projection) +
   ease_aes("cubic-in-out") +
   labs(title = "The World in '{names(projs)[projs == closest_state]}' projection",
        subtitle = "Projection: '{closest_state}'") +
   scale_fill_identity(c('black' = 'black',
                         'red' = 'red')) +
   theme_minimal() +
   theme(axis.title=element_blank(),
         axis.text=element_blank(),
         axis.ticks=element_blank(), 
         panel.grid=element_blank(),
         plot.background=element_rect(fill = "white"))

anim_save("./img/projections.gif", anim, res = 200, width = 1200, height = 675)