Area-honest cartogram — cartogram

Resizes countries by weight (population, GDP, ...) via the optional cartogram package, defeating the "big empty countries dominate the eye" bias of world choropleths.

Usage

cartogram_map(
  data,
  weight,
  type = c("contiguous", "dorling", "noncontiguous", "flow"),
  fill = NULL,
  projection = "equal_earth",
  ...
)

Arguments

data: An sf map-ready frame.
weight: The column to resize by (unquoted).
type: "contiguous" (default), "dorling", "noncontiguous" or "flow". "flow" is the Gastner-Seguy-More flow-based algorithm from the optional cartogramR package – the current state of the art for contiguous cartograms, and seconds rather than minutes where the diffusion-based "contiguous" method is slow.
fill: Optional fill column (unquoted); defaults to weight.
projection: Projection; an equal-area CRS is recommended. See world_map() for the projections available.
...: Passed to the underlying cartogram::cartogram_*() function (e.g. itermax, or k for type = "dorling" – see dorling_map()), or to cartogramR::cartogramR() for type = "flow".

Value

A ggplot object.

Which algorithm

"contiguous" (Dougenik) and "dorling"/"noncontiguous" come from cartogram. "flow" comes from cartogramR and implements the Gastner-Seguy-More flow-based method, which is both the current state of the art and far faster than diffusion-based approaches – prefer it for contiguous cartograms when cartogramR is available.

Cartograms fail quietly: an under-converged one looks plausible while still misrepresenting the areas it exists to make honest. Pass a larger itermax if the result still looks close to the true map.

References

Gastner, M. T., Seguy, V. & More, P. (2018). Fast flow-based algorithm for creating density-equalizing map projections. Proceedings of the National Academy of Sciences 115(10), E2156-E2164. doi:10.1073/pnas.1712674115

Examples

# \donttest{
if (requireNamespace("sf", quietly = TRUE) &&
    requireNamespace("rnaturalearth", quietly = TRUE) &&
    requireNamespace("cartogram", quietly = TRUE)) {
  attach_geometry(countryatlas::world_snapshot$countries, geometry = "sf") |>
    cartogram_map(population, type = "dorling")
}

# }