Create Cartograms with R • cartogram

cartogram is an R package that implements methods for generating continuous area cartograms (based on the rubber sheet distortion algorithm by Dougenik et al., 1985), non-contiguous area cartograms (Olson, 1976), and non-overlapping circles cartograms (Dorling et al., 1996).

Installation

You can install the cartogram package from CRAN as follows:

install.packages("cartogram")

To upgrade to the latest development version of cartogram, install the package remotes and run the following command:

remotes::install_github("sjewo/cartogram")

Examples

Continuous Area Cartogram

library(cartogram)
library(sf)
#> Linking to GEOS 3.13.0, GDAL 3.8.5, PROJ 9.5.1; sf_use_s2() is TRUE
library(tmap)

data("World")

# Keep only the African continent
afr <- World[World$continent == "Africa", ]

# Project the map
afr <- st_transform(afr, 3395)

# Construct continuous area cartogram
afr_cont <- cartogram_cont(afr, "pop_est", itermax = 5)

# Plot the cartogram
tm_shape(afr_cont) +
  tm_polygons("pop_est",
              fill.scale = tm_scale_intervals(style = "jenks")) +
  tm_layout(frame = FALSE,
            legend.position = c("left", "bottom"))

Non-contiguous Area Cartogram

library(cartogram)
library(sf)
library(tmap)

data("World")

# Keep only the African continent
afr <- World[World$continent == "Africa", ]

# Project the map
afr <- st_transform(afr, 3395)

# Plot the original map boundaries
tm_shape(afr) +
  tm_borders() +
  # Add the the cartogram
  tm_shape(cartogram_ncont(afr, "pop_est")) +
  tm_polygons("pop_est",
              fill.scale = tm_scale_intervals(style = "jenks")) +
  tm_layout(frame = FALSE,
            legend.position = c("left", "bottom"))

Non-Overlapping Circles Cartogram

library(cartogram)
library(sf)
library(tmap)

data("World")

# Keep only the African continent
afr <- World[World$continent == "Africa", ]

# Project the map
afr <- st_transform(afr, 3395)

# Plot the original map boundaries
tm_shape(afr) +
  tm_borders() +
  # Add the the cartogram
  tm_shape(cartogram_dorling(afr, "pop_est")) +
  tm_polygons("pop_est",
              fill.scale = tm_scale_intervals(style = "jenks")) +
  tm_layout(frame = FALSE,
            legend.position = c("left", "bottom"))

Use multiple CPU cores

library(cartogram)
library(sf)
library(tmap)
library(future)
library(future.apply)
library(parallelly)
library(progressr)

data("World")

# Keep only the African continent
afr <- World[World$continent == "Africa", ]

# Project the map
afr <- st_transform(afr, 3395)

# Create cartogram using 2 CPU cores on the local machine
# This can speed up computation for larger datasets.
# Set show_progress to TRUE for a progress indicator.
afr_cont <- cartogram_cont(afr, weight = "pop_est",
                            itermax = 5, 
                            n_cpu = 2,
                            show_progress = FALSE)

# Plot the cartogram
tm_shape(afr_cont) +
  tm_polygons("pop_est",
              fill.scale = tm_scale_intervals(style = "jenks")) +
  tm_layout(frame = FALSE,
            legend.position = c("left", "bottom"))

Acknowledgements

The non-contiguous area cartogram and non-overlapping circles cartogram functionalities include major code contributions from @rCarto and @neocarto.

@nowosad contributed to the package by transitioning it to use the sf package and by enhancing the documentation, a task further supported by documentation improvements from @oliveroy.

The functionality to utilize multiple CPU cores was contributed by @e-kotov.

References

This package implements algorithms based on the following seminal works:

Dorling, D. (1996). Area Cartograms: Their Use and Creation. In Concepts and Techniques in Modern Geography (CATMOG), 59.
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. The Professional Geographer, 28: 371–380. doi:10.1111/j.0033-0124.1976.00371.x

cartogram: Create Cartograms with R