Balloon flight should have a higher outlier. The highest balloon parachute/freefall jump was made by Alan Eustace in 2014, who jumped from 135,908 feet (41.425 km). Some others in that range too.
The plot appears to be the ceiling of all data, so those balloon flights are masked by whoever was lolling about on the ISS at the time.
Yeah, that section of the graph is labeled “balloon flights”, only because, for those years, balloons were the highest you could get.
IOW it’s a 3-parameter space (altitude, calendar era, and lofting technology used) being displayed on a 2-dimensional XY plot. Shame he didn’t choose e.g. color as a third discriminator.
But as a practical matter, since the graph is intended to show the "high"lights (heh), the absence of a couple of balloon-coded spikes in the airplane and spaceflight eras isn’t much of an oversight.
No, there wouldn’t be any balloon spikes in the spaceflight era, because at no point in time in the spaceflight era was a balloonist ever the highest human. This is also why the graph doesn’t have a floor, from all of the many people who are on the ground: Neither we nor the space-age balloonists are what’s shown on the graph.
Examining that graph a bit more closely, it has a few down spikes around 1950 that are down below 100 meters. During that era, I doubt there was ever a time that no one was flying above that altitude. Also, there should probably be a few spikes slightly higher in that era to account for the Bell X-1 and early spaceflight.
You got me thinking with this comment …
Spaceflight is interesting. There are two very distinct cases in a dumbbell distribution: the long-term stations and the short term capsule / spaceplane flights with large gaps between.
After a bunch of wiki-ing and working back in time from today towards the dawn of human spaceflight …
The Chinese now have a continuously occupied station from 2022 through today.
ISS has been continually occupied from Nov 2000 through today.
The Soviet Mir had a few gaps in its occupancy: The station was occupied for a total of four distinct periods; 12 March–16 July 1986 (EO-1), 5 February 1987 – 27 April 1989 (EO-2–EO-4), the record-breaking run from 5 September 1989 – 28 August 1999 (EO-5–EO-27), and 4 April–16 June 2000.
Note there’s a short gap between the end of Mir & the start of ISS.
Occupancy of the the earlier Salyut series were also sporadic. As was Skylab. And the farther back in orbital station history the more that’s true.
Punchline being that from Nov 2000 to today there have always been people in LEO. From very roughly 1973 to 2000 there were people on a LEO station a decent fraction of the days (WAG 50%, but with heavier coverage later).
From Gagarin’s first flight in 1961 up through roughly 1973, LEO & suborbital space was far more often empty of people than occupied by even one person.
Thanks for being the impetus to dig all this up. Hope somebody enjoys reading my resulting drivel.
“Can you pass the nackle?”
You can also pronounce “anion” akin to “onion”. And “cation” akin to “cushion”. That always establishes your cutting edge street cred in the rogue chemist / mad scientist world
So more “Breaking Mad” than “Breaking Bad”. 
Seriously, here in the real world when I read “NaCl” I mentally pronounce it “nackle” and always have. Even though I’ve known what it really means from a very young age.
What compound gives the pronunciation “choochoo”?
Our most recent cat had been nicknamed “cation” by the rescue lady. She was using various atomic terms for her cats at the time (one tends to run out of names in these situations) and we happened to get the one that was more apt that the others.
Acetic_acid (sorry, preview not working well)
I would pronounce that like “caution”.
Acetic acid is the 2nd compound in the comic (CH3COOH), pronounced chuckoo.
If you are OK with ignoring standard nomenclature, you could go with oxalic acid. It’s properly written C2H2O4 or COOH-COOH, but if you’re already pissing off chemists, go ahead and write it as CHOO-CHOO.
Oops, misread the ask (again)
Brian
So why is the audience shouting ‘Nitric oxide’?
My point was the “sh” sound in the middle, not which vowel. So another way to write my proposed pronunciation is “CASH’n”.
Rhymes with ration. Or maybe nation.
That was how I did it. To universal “acclaim” from my better-informed fellow college kids. 