---
title: "Plot Prefectural Choropleth Maps"
description: "Join prefecture-level GDP data to a Japan map and map one fill variable."
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Plot Prefectural Choropleth Maps}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  message = FALSE,
  fig.width = 7,
  fig.height = 5,
  dpi = 120,
  fig.bg = "white",
  dev.args = list(bg = "white")
)
jpmap_build_full_vignettes <- identical(tolower(Sys.getenv("JPMAP_FULL_VIGNETTES")), "true") ||
  identical(tolower(Sys.getenv("IN_PKGDOWN")), "true")
jpmap_has_boundary_data <- jpmap_build_full_vignettes &&
  nrow(jpmap::available_jpmap_data()) > 0
```

This example uses `jp_prefecture_gdp`, a bundled prefecture-level GDP dataset.
The map uses one fill variable: GDP per capita in Japanese yen.

```{r}
library(tidyverse)
library(jpmap)

gdp <- jp_prefecture_gdp |>
  select(pref_code, prefecture, gdp_per_capita_jpy)
```

```{r prefectural-gdp, eval = jpmap_has_boundary_data}
plot_jpmap(
  "prefecture",
  data = gdp,
  values = "gdp_per_capita_jpy",
  color = "grey35",
  linewidth = 0.25
) +
  scale_fill_gradient(
    low = "#D9E8FF",
    high = "#001040",
    name = "GDP per capita\n(JPY)"
  ) +
  labs(
    title = "Prefecture GDP per capita",
    caption = "GDP data: OECD 2021 values tabulated on Wikipedia."
  ) +
  theme(
    legend.background = element_rect(fill = "white", color = NA),
    plot.title = element_text(face = "bold", color = "#001040"),
    plot.caption = element_text(color = "#2C2A29", hjust = 0, size = 8)
  )
```

`plot_jpmap()` joins by a shared column. Here both the map and `gdp` have
`pref_code`, so no extra join argument is needed.