Quick R: Inset maps

How to place an inset map in R? There are many solutions out there using the ggplot2 package (see Drawing beautiful maps programmatically with R , sf and ggplot2 by Mel Moreno and Mathieu Basille). However, I like the old reliable plot function, so the question is: is there another way?

There is. I found inspiration here and I just applied it to a map.

Required R packages

library(sf)
library(dplyr)
library(rnaturalearth)

Mimicking Moreno & Basille

I present here an alternative version of Drawing beautiful maps programmatically with R, sf and ggplot2, so the bulk of the detail can be found there. I focus only on the plot() side.

world <- ne_countries(scale = "medium", returnclass = "sf")
USA <- subset(world, admin == "United States of America")

# Plot mainland USA----
par(mar = c(0, 0, 0, 0))
plot(
  st_geometry(world %>%
    st_transform(2163)),
  xlim = c(-2500000, 2500000),
  ylim = c(-2300000, 730000),
  col = "#F6E1B9",
  border = "#646464",
  bg = "#C6ECFF"
)
plot(
  st_geometry(USA) %>% st_transform(2163),
  col = "#FEFEE9",
  border = "black",
  add = T
)

# Plot Alaska----
plot(
  st_geometry(world %>%
    st_transform(3467)),
  xlim = c(-2400000, 1600000),
  ylim = c(200000, 2500000),
  col = "#F6E1B9",
  border = "#646464",
  bg = "#C6ECFF"
)
plot(
  st_geometry(USA) %>% st_transform(3467),
  col = "#FEFEE9",
  border = "black",
  add = T
)

# Plot Hawaii----
plot(
  st_geometry(world %>%
    st_transform(4135)),
  xlim = c(-161, -154),
  ylim = c(18, 23),
  col = "#F6E1B9",
  border = "#646464",
  bg = "#C6ECFF"
)
plot(
  st_geometry(USA) %>% st_transform(4135),
  col = "#FEFEE9",
  border = "black",
  add = T
)

Insetting

From now on, I focus on the inset part, using the fig argument of par(). Quoting statmethods:

(…) think of the full graph area as going from (0,0) in the lower left corner to (1,1) in the upper right corner. The format of the fig= parameter is a numerical vector of the form c(x1, x2, y1, y2) (…) fig= starts a new plot, so to add to an existing plot use new=TRUE.

With x1 and y1 as the starting points and x2, y2 as the final points, we can set up those parameters and adjust the final placement of the insets. Additionally, I added a box around the insets using bbox(). I didn’t mimic Moreno & Basille here and I just worked it out by myself.

par(mar = c(0, 0, 0, 0))
plot(
  st_geometry(world %>%
    st_transform(2163)),
  xlim = c(-2500000, 2500000),
  ylim = c(-2300000, 730000),
  col = "#F6E1B9",
  border = "#646464",
  bg = "#C6ECFF"
)
plot(
  st_geometry(USA) %>% st_transform(2163),
  col = "#FEFEE9",
  border = "black",
  add = T
)
# Alaska
par(
  fig = c(0.01, 0.28, 0.01, 0.33),
  new = TRUE
)
plot(
  st_geometry(world %>%
    st_transform(3467)),
  xlim = c(-2400000, 1600000),
  ylim = c(200000, 2500000),
  col = "#F6E1B9",
  border = "#646464",
  bg = "#C6ECFF"
)
plot(
  st_geometry(USA) %>% st_transform(3467),
  col = "#FEFEE9",
  border = "black",
  add = T
)
box(which = "figure", lwd = 1)

# Hawaii
par(
  fig = c(0.29, 0.45, 0.01, 0.15),
  new = TRUE
)
plot(
  st_geometry(world %>%
    st_transform(4135)),
  xlim = c(-161, -154),
  ylim = c(18, 23),
  col = "#F6E1B9",
  border = "#646464",
  bg = "#C6ECFF"
)
plot(
  st_geometry(USA) %>% st_transform(4135),
  col = "#FEFEE9",
  border = "black",
  add = T
)

box(which = "figure", lwd = 1)

Results may vary depending on the size of the original plot (Mainland USA), your plotting device and the output. However, with a bit of trial and error, it is quite easy to adjust the final result.

As an example, see one of my contributions to Wikimedia Commons , which represents a map of the NUTS3 regions of the European Union. Several countries (France, Portugal, Spain) have overseas territories, so I made a few insets on the right side.