title: Cartogram + choropleth map in R
body: <p>I've been using ggplot2 lately to create a bunch of choropleths.  I was wondering if it was possible to use ggplot2 to create a map similar to this (from <a href="http://www.worldmapper.org/textindex/text_index.html" rel="noreferrer">WorldMapper</a>):</p>
  
  <p><img src="https://i.stack.imgur.com/2qwpw.png" alt="enter image description here"></p>
  
  <p>It's a choropleth where the shapefile polygons are distorted to represent relative population counts.  I believe this is called a cartogram.  They do this with a bunch of other variables.  In the spirit of the <a href="http://blog.revolutionanalytics.com/2009/11/choropleth-map-r-challenge.html" rel="noreferrer">Choropleth R Challenge</a>, does anyone know how to do this using R?</p>