Align edges of ggplot choropleth (legend title varies)

Question

I am attempting to align the left and right edges of 4 ggplot choropleth maps using this method. I am unable to do this though.

Original plot:

Answer 1

Here is an example:

library(gtable)
grid.draw(cbind(rbind(p1, p2, size="last"), rbind(p3, p4, size="last"), size = "first"))

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Updated

This is a bad hack so I don't recommend to use. Probably this will not work in future.

gt <- cbind(rbind(p1, p2, size="last"), rbind(p3, p4, size="last"), size = "first")
for (i in which(gt$layout$name == "guide-box")) {
  gt$grobs[[i]] <- gt$grobs[[i]]$grobs[[1]]
}
grid.draw(gt)

Answer 2

Using cowplot package:

library(cowplot)
plot_grid(plot1, plot3, plot2, plot4, ncol = 2, align = "v")