For a couple of decades now we've had maps of the cosmic web as traced by galaxy positions from redshift surveys like the 2dfgrs:
Are there any similar maps which rely on gaseous tracers? I guess this should be impossible with current observatories in neutral hydrogen (21-cm emission) because it is too faint, and ionized gas in emission is also difficult in this regime, I think? There's always the Ly-$\alpha$ forest in absorption, but is there a sufficiently dense population of background sources to make maps of specific sky patches, or are only statistics of the web based on relatively isolated sight lines possible?
In the end, what is the best map of the cosmic web directly tracing gas (emission or absorption) currently available?