They employ a technique called a cartogram, which in this case displays country boundaries, thematically altered by size - based on another demographic variable of interest. In short, the bigger or smaller the shape, the larger or smaller the variable being mapped.
http://www.sasi.group.shef.ac.uk/worldmapper/index.html
Of particular interest in today's political environment are two image examples.
Refugee Origin
Net Immigration
There are wonderful map
presentations on their site.
Check them out.
