ggplot: How to increase spacing between faceted plots?

Question

I have several faceted histograms (obtained with the command below) which are nicely plotted one under the other. I would like to increase the spacing between them, however, they are tight.

I looked at the doc but didn't find a parameter for this.

Thanks in advance.

qplot (Happiness.Level, Number.of.Answers, data=mydata, geom="histogram") + facet_grid (Location ~ .) 

Answer 1

Try something like this

p + opts(panel.margin = unit(2, "lines"))

See also here: Slicing plots generated by ggplot2