It's a plot of nearby stars, with lines indicating which TV show signals are just now reaching them. It's from Abstruse Goose, which is a new fav for me. Plus they have a free eBook of the first 100 comics. And their website is minimalist. Enjoy!
Conceptually, it's an elegant mashup. Take a star map, which has distances to nearby stars in light-years (distance light travels in one year). Since radio waves are EM waves, same as visible light, they travel (ta da!) one light year in one year. So if a star is 3 light years away, it's getting signals we sent out 3 years ago. By converting distances to past transmission dates, presto, we get the map!
Alex, the daytime astronomer