Two-dimensional projection of a slice of thickness 50 Mpc in the xy plane of the TNG300-1 box. The red points correspond to gas cells within the R₂₀₀ radii of nodes (traced in this work by the DisPerSE maximum density critical points, see Sect. 2.3). The blue points represent gas around filaments, at distances closer than 1 Mpc from the spine of the cosmic web. Finally, the green points show gas in the R₂₀₀ region of galactic haloes (i.e. within spheres of radius 1 × R₂₀₀). The galactic haloes residing in filaments are clearly apparent (green over blue regions). The centres of the cells are plotted as points, but the TNG300-1 simulation is described by Voronoi cells having various volumes.