I didn’t watch the video. I examined previews step by step until I saw all the Voronoi³ points get flattened by the Graph Mapper, so I bypassed it by connecting PopGeo directly to Voronoi³:
Then I noticed that the ReMap feeding Graph Mapper needed to have its ‘S’ (Source) input defined by connecting it to Bnd (Bounds) and its output remapped to ‘Z’.
Voronoi_2021_Jul2a.gh (22.7 KB)
Now you can play with Graph Mapper to change the effect, getting the larger holes at the bottom:
Voronoi_2021_Jul2b.gh (22.7 KB)