Notice that we create a graph per continent by setting
facets = ~continent. The tilde there is important—it’s a one-sided formula. You could also write
c("continent")if that’s clearer to you.
I also set the number of columns, guaranteeing that we see no more than 3 columns of grids. I could alternatively set
nrow, which would guarantee we see no more than a certain number of rows.
There are a couple other interesting features in facet_wrap. First, we can set
scales = "free"if we want to draw each grid as if the others did not exist. By default, we use a scale of “fixed” to ensure that everything plots on the same scale. I prefer that for this exercise because it lets us more easily see those continental clusters.
Facets let you compare multiple graphs quickly. They’re great for fast comparison, but as I show in the post, you can distort the way the data looks by lining it up horizontally or vertically.