Somehow, somewhere I stumbled across the image at right which, if you click it, takes you to more detailed version. If that one’s not big enough, try this one.
The map is the stellar work of Hamcall.net, which boasts the largest and best-kept database of amateur radio operators by callsign available online (and would never condone unlicensed operation, of course).
The next step of coolness would be animating this map over time. I wonder if they have similar maps of previous years.