tm_cartogram: Map layer: cartogram

In tmap.cartogram: Extension to 'tmap' for Creating Cartograms

Map layer: cartogram

Description

Map layer that draws a cartogram. See details for types. It is recommended to specify a proper crs in [tmap::tm_shape()].

Usage

tm_cartogram(
  size = 1,
  size.scale = tmap::tm_scale(),
  size.legend = tmap::tm_legend_hide(),
  size.chart = tmap::tm_chart_none(),
  size.free = NA,
  plot.order = tmap::tm_plot_order("size", reverse = FALSE),
  options = opt_tm_cartogram(),
  ...
)

tm_cartogram_ncont(
  size = 1,
  size.scale = tm_scale(),
  size.legend = tm_legend_hide(),
  size.chart = tm_chart_none(),
  size.free = NA,
  plot.order = tm_plot_order("size", reverse = FALSE),
  options = opt_tm_cartogram_ncont(),
  ...
)

tm_cartogram_dorling(
  size = 1,
  size.scale = tm_scale(),
  size.legend = tm_legend_hide(),
  size.chart = tm_chart_none(),
  size.free = NA,
  plot.order = tm_plot_order("size", reverse = FALSE),
  options = opt_tm_cartogram_dorling(),
  ...
)

opt_tm_cartogram(type = "cont", itermax = 15, ...)

opt_tm_cartogram_ncont(type = "ncont", expansion = 1, inplace = FALSE, ...)

opt_tm_cartogram_dorling(type = "dorling", share = 5, itermax = 1000, ...)

Arguments

size, size.scale, size.legend, size.chart, size.free	Visual variable that specifies the polygon sizes.
plot.order	Specification in which order the spatial features are drawn. See [tmap:tm_plot_order()] for details.
options	passed on to the corresponding 'opt_<layer_function>' function
...	arguments passed on to [cartogram::cartogram_cont()]
type	cartogram type, one of: "cont" for contiguous cartogram, "ncont" for non-contiguous cartogram and "dorling" for Dorling cartograms
itermax	maximum number of iterations (see [cartogram::cartogram_cont()])
expansion	factor expansion, see [cartogram::cartogram_ncont()] (argument 'k')
inplace	should each polygon be modified in its original place? ('TRUE' by default)
share	share of the bounding box filled with the larger circle (see [cartogram::cartogram_dorling()] argument 'k')

Details

In the contiguous cartogram polygons are distorted where the geographic relations are maintained. The algorithm by Dougenik et al. (1985) is used via [cartogram::cartogram_cont()].

In the non-contiguous cartogram polygons are resized only. The used algorithm has been proposed by Olson (1976) and implemented in [cartogram::cartogram_ncont()].

The Dorling cartogram (Dorling, 1996) generates proportional bubbles and is implemented in [cartogram::cartogram_dorling()].

Value

a [tmap::tmap-element], supposed to be stacked after [tmap::tm_shape()] using the '+' operator. The 'opt_<layer_function>' function returns a list that should be passed on to the 'options' argument.

References

Dougenik, J. A., Chrisman, N. R., & Niemeyer, D. R. (1985). An Algorithm To Construct Continuous Area Cartograms. In The Professional Geographer, 37(1), 75-81.

Olson, J. M. (1976). Noncontiguous Area Cartograms. In The Professional Geographer, 28(4), 371-380.

Dorling, D. (1996). Area Cartograms: Their Use and Creation. In Concepts and Techniques in Modern Geography (CATMOG), 59.

Examples

library(tmap)

Africa = World[World$continent == "Africa", ]

tm_shape(Africa, crs = "+proj=robin") +
  tm_cartogram_ncont(size = "pop_est", options = opt_tm_cartogram_ncont())


tm_shape(Africa, crs = "+proj=robin") +
  tm_cartogram(size = "pop_est", options = opt_tm_cartogram(itermax = 15))

tm_shape(World, crs = "+proj=robin") +
  tm_polygons() +
  tm_cartogram_ncont(size = "pop_est", fill = "yellow")

tmap.cartogram documentation built on April 4, 2025, 12:35 a.m.