it is a combination, but not voronoi. i am using midrange contours from one of my middle tier heightmap noise octaves to make those "roads". so it's that mixed with a curve on the terrain height (which gives us a combination of coastline population, mountain remoteness, and water nonpopulation) and also i'm subtracting near the poles and then mixing everything with two octaves of random noise (a low frequency one to clump "cities" and a very high frequency to make individual points of light)