The map was put together by Barbara Ricci at the University of Ferrara in Italy. The arXiv blog explains how it was made:
These guys take data from the International Agency of Atomic Energy giving the thermal power of every reactor on the planet. That gives Ricci and co a good idea of how many antineutrinos each reactor core produces and allowed them to calculate the antineutrino flux all over the world.
Next, they considered an antineutrino detector containing 10^32 protons and calculated how many antineutrinos from reactor cores this device would spot over the course of a year.
Finally, they plotted their results for the entire planet showing the areas where the background signal for any antineutrino detector would be highest. You can see the map here ( 1 TNU= 1 event/yr/10^32 detector protons ).
It's an interesting map—and not perhaps for the reason you expect. In fact, scientists are keen to use antineutrino measurement to understand how the Earth generates heat. The decay of radioactive elements—such as potassium-40 or thorium-232—in the Earth's interior are thought to generate much of the Earth's heat—and, in turn, produce antineutrinos.
Geophysicists reckon that by measuring antineutrino counts across the globe, they can gain a better understanding of the heat that our planet generates—but all the noise introduced by nuclear plants currently makes it impossible. This map will allow them to work out the true signal, and even choose locations which allow them to spot antineutrinos interferences-free, like in Hawaii. Which is cool. Or not, as the case may be. [arXiv]