geoviz_hexagonal-choropleth.Rmd

---
title: "Charts: Hexagonal Choropleth"
output:
  html_document:
    toc: true
    toc_float:
      collapsed: false
    includes:
      before_body: [includes/include_header.html, includes/include_header_navpage.html]
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---

## What is a hexagonal choropleth (or a tilegram)?

Hexagonal Choropleth are choropleth where regions are converted into equally sized hexagons and each is coloured according to either a discrete or continuous variable. More generally these visualisations are called <strong>tilegrams</strong>, where the regions can be any <em>regular polygon</em> but hexagons are amongst one of the most flexible shapes for these maps. The process of converting shapefiles to regular polygons that are positioned in such a way to still retain the shape of the original geographic regions is complicated, and typically requires manual hand tuning.

Required Data:

- Hexagonal Regions: Enclosed hexagonal regions, i.e. topologically closed polygons, sometimes called convex hulls. For instance the subregions within a country, i.e. the states of the USA.
- Values: Discrete or categorical values for each enclosed region, for instance the population of each state or the division to which the state belongs.

Below is a minimal example of a hexagonal choropleth built using `R` and the `leaflet` library, inspired by this [tutorial on `tilegramsR`](http://rpubs.com/bhaskarvk/tilegramsR)



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

states_info <- shp_all_us_states
st_geometry(states_info) <- NULL


NPR1to1 <- st_as_sf(NPR1to1) %>%
  left_join(states_info, by = c("state" = "state.short.name"))

palette_state_division <- colorFactor("Paired", unique(NPR1to1$state.division))

leaflet(
  NPR1to1,
  options=leafletOptions(
    crs = leafletCRS("L.CRS.Simple"),
    minZoom = -3, maxZoom = -3,
    dragging = FALSE, zoomControl = FALSE,
    attributionControl = FALSE),
  width = "250px", height = "250px"
  ) %>%
  addPolygons(
    weight=2,
    color='#000000', group = 'states',
    fillOpacity = 0.6, opacity = 1, fillColor= ~palette_state_division(state.division),
    highlightOptions = highlightOptions(weight = 4),
    label = ~paste0(state, " (", state.division, ")")
    ) 
```