Ternary choropleth for three-part compositions

Colours each country by the balance of three parts of a whole: the agriculture, industry and services shares of GDP, or the young, working-age and old shares of a population. Each part has a primary colour, and a country's colour mixes the three in proportion to its shares, so a country dominated by one part takes that part's colour and an even mix is grey (the ternary balance scheme).

Usage

ternary_map(
  data,
  x,
  y,
  z,
  centre = TRUE,
  projection = "equal_earth",
  recenter = NULL,
  hue = 80,
  key = TRUE,
  title = NULL,
  legend = NULL,
  footnote = "auto"
)

Arguments

data: A map-ready frame from attach_geometry(), on either backend.
x, y, z: The three parts (unquoted), each non-negative. They are closed to shares, so counts and percentages work as well as proportions. A country missing any part, or with all three zero, is drawn as no data.
centre: TRUE (default) to centre on the average composition, the closed geometric mean over the countries with all three parts above zero; three positive numbers, a composition to centre on, in the order x, y, z; or FALSE for the plain scheme, where grey means equal shares.
projection, recenter: As in world_map().
hue: The hue of x's colour, in degrees on the HCL wheel; y and z take the hues 120 and 240 degrees on.
key: Draw the colour triangle in the legend area? Needs ggplot2 3.5.0 or later.
title, legend: Optional plot title and key title.
footnote: The caption, as in world_map(): "auto" (default) states the coverage, the centre and the source, a string is used as given, FALSE adds nothing.

Value

A ggplot object. map_provenance() records the centre.

Details

Countries' compositions usually sit close together, and on the plain scheme they come out in near-identical colours. centre = TRUE (the default) centres the scheme on the average composition (Schoeley 2021): grey is the average country, and a colour says which part a country has more of than the average. The key is the colour triangle with every country on it as a ring, and the caption states the average composition the colours are relative to.

References

Schoeley, J. (2021). The centered ternary balance scheme: a technique to visualize surfaces of unbalanced three-part compositions. Demographic Research 44(19), 443-458. doi:10.4054/DemRes.2021.44.19

Examples

# \donttest{
# A made-up composition: three parts that add up to each country's total.
snap <- countryatlas::world_snapshot$countries
set.seed(1)
snap$a <- stats::runif(nrow(snap), 1, 4)
snap$b <- stats::runif(nrow(snap), 2, 6)
snap$c <- stats::runif(nrow(snap), 4, 9)
ternary_map(attach_geometry(snap), a, b, c)

# }