Geometry of the simple model, in which we treat the cosmic web as a collection of randomly displaced cubic unit cells. We show one face (grey square) of a unit cell, with edges of comoving length l. Filaments of typical comoving width w_f and length l_f ≔ l − w_f cover the light-blue–shaded region of the face, and extend to the faces of neighbouring unit cells (grey dashed lines). Where filaments meet, galaxy clusters reside (orange-shaded regions), each of which is also connected to a filament oriented away from the observer. The central part of the face represents a sheet (dark blue), behind which a large void looms (not depicted). The figure is not to scale: filament widths are exaggerated compared to realistic filament lengths.