Day 3: polygon

Day 3 of the challenge is polygons, so I wanted to work out how make a map that splits NZ into regions and fills the area of each by population. The spData package was a good find because it contains data about land area, population, and median income data by region. The population data was a bit out of date so here I have found 2024 estimates from StatsNZ and joined the updated population data.

get data

library(tidyverse)
library(here)
library(sf)
library(spData) # has nz map/data
library(janitor)
library(scales)

nz <- nz 

nz_regions <- nz %>%
  select(Name, geom)


# Stats NZ subnational population estimates (RC, constituency), by age and sex, at 30 June 2023-24 (2023 boundaries)
# clean to get more recent data, remove totals, name variable names match nz df so that join works

pop <- read_csv(here("maps", "2025-11-03_polygon", "statsNZ_pop_region.csv")) %>%
  clean_names() 

pop_total <- pop %>%
  filter(area == "Total New Zealand by regional councils") %>%
  filter(year_at_30_june == 2024)

totalNZpop24 <- pop_total$obs_value

pop_region <- pop %>%
  filter(year_at_30_june == 2024) %>%
  filter(area != "Total New Zealand by regional councils") %>%
  select(Name = area, Population24 = obs_value) %>%
  mutate(Name = str_remove(Name, "region")) %>%
  mutate(Name = str_trim(Name)) %>%
  mutate(Name =  str_replace_all(Name, "ū", "u")) %>% 
  mutate(Name =  str_replace_all(Name, "Wh", "W"))


# note: when joining always put the sf dataframe first, so that it keeps geom info

nzpop24 <- left_join(nz, pop_region, by = "Name") %>%
  rowwise() %>%
  mutate(proportion = (Population24/totalNZpop24)*100)

northsouth <- nzpop24 %>%
  group_by(Island) %>%
  summarise(pop = sum(proportion))

plot

ggplot(data = nz) +
  geom_sf(aes(fill = Name), color = "black") + 
  labs(title = "Map of New Zealand Regions", fill = "Region Name") +
  theme_bw() 

ggplot(data = nzpop24) +
  geom_sf(aes(fill = Population24), color = "black") + # Fill by region name and add black borders
  labs(title = "The Team of 5 million", fill = "Population", 
       subtitle = "StatsNZ estimates that 5.3 million people live in New Zealand. \nOne third of Kiwis live in Auckland. \nMore than 75% of Kiwis live in the North Island.", 
       caption = "Data from StatsNZ Dec 2024") +
  scale_fill_gradient(low = "lightblue", high = "darkblue", 
                      labels = label_number(scale = 1e-6, suffix = "M")) +
  theme_bw()