geoviz_choropleth.Rmd

---
title: "Geoviz: Choropleth"
output:
  html_document:
    toc: true
    toc_float:
      collapsed: false
    includes:
      before_body: [includes/include_header.html, includes/include_header_navpage.html]
editor_options: 
  chunk_output_type: console
---
# What is a choropleth?

Choropleth are extremely useful visualisations to visually compare the differences between geographic regions, for either discrete and continuous variables. 

Required Data:

- Shapefiles: Enclosed regions, i.e. topologically closed polygons, sometimes called convex hulls. For instance, country borders.
- Values: Discrete or categorical values for each enclosed region, for instance the population of a country or membership of the UN

Below is a minimal example using `R` and the `leaflet` library:

```{r, echo=FALSE, message=FALSE, warning=FALSE, paged.print=FALSE}
library("tidyverse")
library("leaflet")
library("sf")
library("gapminder")

geojson_worldmap <- st_read("https://raw.githubusercontent.com/johan/world.geo.json/master/countries.geo.json",
                            quiet = TRUE)
geojson_worldmap <- invisible(geojson_worldmap %>%
  left_join(gapminder %>%
               filter(year == max(year)) , by = c("name" = "country")) %>%
  filter(name != "Antarctica"))
palette_pop <- colorNumeric("YlOrBr" , geojson_worldmap$pop, na.color = "#c0c1c4")
geojson_worldmap %>%
  leaflet(width = "300px",
          height = "200px") %>%
  addPolygons(fillColor = ~palette_pop(pop),
              fillOpacity = 0.8,
              color = "#000",
              weight = 1,
              label = ~name)
```