#30DayMapChalleng 2021 - Day 24 - Historical

onions.R

# Make a world map of exports from NZ, with Pacific centred
# For #30DayMapChallenge 2021 - Day 24 - Historical
#  -- David Friggens, November 2021

# Map style inspired by @richard_vogg
# https://github.com/richardvogg/30DayMapChallenge21

library(magrittr)
library(readxl)
library(dplyr)
library(sf)
library(countrycode)
library(rnaturalearth)
library(ggplot2)
library(ggflags)
library(ggrepel)

PLOT_FONT <- "Nunito Sans"
BG_COLOUR <- "grey20"
LAND_COLOUR <- "white"
LINE_COLOUR <- "#dfbf81"

# Data from my colleague, but originally from Stats NZ
onions <- 
  read_excel("trade/Export charts for report.xlsx",
             sheet = "Top 20 countries",
             range = "A5:B50",
             col_names = FALSE) %>% 
  set_names(c("country", "value")) %>% 
  mutate(value = round(value / 1000000, 1)) %>% 
  arrange(desc(value)) %>% 
  head(20) %>% 
  mutate(iso_a3 = countrycode(country, origin = "country.name", destination = "iso3c"))

# Medium needed for get coordinates for small countries
# But I'll only plot the small scale

world_medium <-
  ne_countries(scale = "medium", returnclass = "sf") %>%
  filter(iso_a3 != "ATA") %>% #filter out Antartica
  select(sovereignt, continent, iso_a3)

world_small <-
  ne_countries(scale = "small", returnclass = "sf") %>%
  filter(iso_a3 != "ATA") %>% #filter out Antartica
  select(sovereignt, continent, iso_a3)

# Get coordinates of countries for lines and circles

nz_c <- 
  world_medium %>% 
  filter(iso_a3 == "NZL") %>% 
  st_centroid() %>% 
  select(nzl = iso_a3,
         nzl_c = geometry)

destination_c <- 
  world_medium %>% 
  inner_join(onions, by = "iso_a3") %>% 
  st_centroid(of_largest_polygon = TRUE) %>% 
  # ISO2 needed for flags
  mutate(iso_a2 = iso_a3 %>% countrycode(origin = "iso3c", destination = "iso2c") %>% str_to_lower(),
         exports_display = glue("${value}m")) %>% 
  select(iso_a3,
         iso_a2,
         exports = value,
         exports_display,
         dest_c = geometry)

# Easy to make straight lines...

onion_lines <- 
  onions %>% 
  mutate(nzl = "NZL") %>% 
  inner_join(nz_c, by = "nzl") %>% 
  inner_join(destination_c, by = "iso_a3") %>% 
  rowwise() %>% 
  mutate(geom = st_union(nzl_c, dest_c) %>% st_cast("LINESTRING")) %>% 
  ungroup() %>% 
  select(-nzl_c, -dest_c) %>%
  st_as_sf()

# ...and surprisingly easy to turn them into great circles!
# Thanks Jesse Sadler https://www.jessesadler.com/post/great-circles-sp-sf/

onion_gc_lines <- 
  onion_lines %>% 
  st_segmentize(units::set_units(20, km))

# Easy to recentre the projection but it is a disaster if any polygons are split.
# I'm sure I saw a blog post recently that mentioned how to fix it, but can't find it now.
# But since I don't need Greenland or Iceland it's easy enough just to take them out. :-)

world_small2 <- 
  world_small %>% 
  filter(! iso_a3 %in% c("GRL", "ISL")) %>% 
  st_transform("+proj=patterson +lon_0=160")


# proportionately sized circles were ok, but tricky with labels
# but proportionately sized flags were no good

gg_onion <- 
  ggplot() +
  geom_sf(data = world_small2,
          fill = LAND_COLOUR,
          size = 0.1) +
  geom_sf(data = onion_gc_lines,
          colour = LINE_COLOUR) +
  # geom_sf(data = destination_c,
  #         aes(size = exports),
  #         colour = LINE_COLOUR) +
  geom_label_repel(data = destination_c,
                   stat = "sf_coordinates",
                   aes(label = exports_display,
                       geometry = dest_c),
                   size = 10,
                   family = PLOT_FONT,
                   colour = BG_COLOUR) +
  geom_flag(data = destination_c,
            stat = "sf_coordinates",
            aes(country = iso_a2,
                geometry = dest_c),
            size = 12) +
  coord_sf(datum = NA) +
  labs(title = "New Zealand Onion Exports 2020: Top 20 Countries (94%)",
       subtitle = "#30DayMapChallenge 20201 - Day 24 - Historical",
       caption = "Map: David Friggens @dakvid. Data: StatsNZ",
       x = NULL, y = NULL) +
  theme_bw() +
  theme(plot.background = element_rect(fill = BG_COLOUR, colour = BG_COLOUR),
        panel.background = element_rect(fill = BG_COLOUR, colour = BG_COLOUR),
        legend.position = "none",
        plot.title = element_text(size = 72, family = PLOT_FONT, colour = LINE_COLOUR, hjust = 0.5),
        plot.subtitle = element_text(size = 32, family = PLOT_FONT, colour = LINE_COLOUR, hjust = 0.5),
        plot.caption = element_text(size = 28, family = PLOT_FONT, colour = LINE_COLOUR))

ggsave(plot = gg_onion,
       path = "Day_24", filename = "Day_24_onions.png", device = "png",
       width = 40, height = 20, dpi = 72)