I don't like it when delta-v maps include atmospheric drag, because the numbers depend on how aerodynamic your rocket is, in contrast to the other manoeuvres where the amount of delta-v doesn't depend on the type of rocket you have at all.
Skimming the thread, they made "assumptions" for cases like taking off from bodies with atmosphere.
Here is more on how they came up with the number for Venus, including some actual math: https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of....
The OG image mentions that there are assumptions being made. The image linked by GP is a derivative work, improving on and crediting the work of /u/CuriousMetaphor, however it omits some of the caveats in the legend.
> I don't like it when delta-v maps include atmospheric drag
Yes, I find it quite unintuitive, especially as the map is now asymmetric: if you take into account drag on liftoff, you would also take into account aerobraking for reentry. It means that the map can't really be used for body-to-body calculations, as it assumes "rocket liftoff" for the low orbit<->surface transition.
Ideally, atmospheric parameters should be specified some other way on the map, or it could branch to show both liftoff and reentry costs on each body (and possibly delta-v due only to gravity).
Reentry delta-V isn't really well-posed. The delta V that would enter orbit, or even less, with a somewhat different angle reenters. So the "reentry delta V" might very possibly be negative, in that you could go Earth LEO to body surface with less velocity change.
> possibly delta-v due only to gravity)
Now, that's more useful to have around.