The first image jumped out at me because the author chose to use blue and red which, when used on a map of the United States always indicates political affiliation, but the areas that were marked "red" and "blue" were reversed from what my expectation was (coasts and cities red, midwest + great plains blue).

> A county like San Francisco or New York, which packs thousands of residents into a small area, now stands out with an intense color saturation, drawing the eye immediately to where the people actually are. Conversely, a vast county with a sparse population adopts a lighter tone, accurately reflecting its lower density without the distraction of an oversized area.

(Emphasis on "saturation" added.) This isn't quite right, the most-densely populated hexes (large cities) are a pretty saturated red color yes, but the least-densely populated hexes (west Texas) are a pretty saturated blue color. In fact, this color palette makes it really difficult to see what the author intends.

> Using the size of counties as a dimension to represent population can also showcase population centers and free up the color dimension to show another dimension like population density.

Ok yeah that's a cartogram, I know how to expect that to look... wait, no, the image has the same center points for every county, a hexagon outline drawn around that, and then a confusingly-colored solid circle painted over each. The colors are confusing because the overwhelming effect is that the hex outlines dominate the perception of the dark blue nearly-point-sized "circles" in the majority of the map.

Look at Nevada. On the first map Clark County (where Las Vegas is) is a light blue colored hex in a state of mostly dark blue hexes and Washoe County (where Reno is) is light red. On the second map Clark is the largest light blue circle in the state and Washoe is a smaller light blue circle, which seems to be the reverse of what the first map says. ...Also, Washoe appears to be in a different place maybe? It seems to have moved north a hex.

I'm not just picking nits, this is difficult stuff, but an extremely powerful way to convey a ton of densely-packed (no pun intended) information, when done right. See, for instance [0][1][2][3] all by Edward Tufte.

[0] "The Visual Display of Quantitative Information" https://www.amazon.com/Visual-Display-Quantitative-Informati...

[1] "Visual Explanations: Images and Quantities, Evidence and Narrative" https://www.amazon.com/dp/0961392126

[2] "Beautiful Evidence" https://www.amazon.com/dp/0961392177

[3] "Envisioning Information" https://www.amazon.com/Envisioning-Information-Edward-R-Tuft...

"Proofiness" : https://www.amazon.com/Proofiness-Youre-Being-Fooled-Numbers...

It is also a common tread in books by Tufte : https://en.wikipedia.org/wiki/Edward_Tufte

I like "Visual Explanations: Images and Quantities, Evidence and Narrative" : https://www.amazon.com/Visual-Explanations-Quantities-Eviden...