File this one under “Unfamiliar Words for Familiar Concepts,” “Words That Are Missing from the Big Dictionaries,” and “Fun with Greek.”
I know a few cartographic categories: topographic, thematic, political, economic, and so on. But I’d never encountered choropleth until last week, when I came across it on Twitter.
First genuinely surprising choropleth I’ve seen in a long time. pic.twitter.com/YmBT9pUMYQ— Dr. Brian Keegan (@bkeegan) May 20, 2021
I couldn’t find choropleth in the OED, or in Merriam-Webster online, or in Wordnik. It isn’t even in my massive Webster’s Third New International (1986), which does include a related word, chorography: “the art of describing a particular region of district.”
A choropleth map (from Greek χῶρος choros 'area/region' and πλῆθος plethos 'multitude') is a type of thematic map in which a set of pre-defined areas is colored or patterned in proportion to a statistical variable that represents an aggregate summary of a geographic characteristic within each area, such as population density or per-capita income.
I know at least one other plethos word: plethora (“overabundance”). I was confused, though, by choros, which I guessed was related to choreography. But no: choreography comes to us from a different Greek root, choreia (χορεία), which means “circular dance” and which spread throughout the Balkans and Asia Minor as something sounding like hora, like the Jewish circle dance. Choreia is also the source of chorus.
Back to choros now.
A choropleth map of the US that summarizes the results of the 2008, 2012, 2016, and 2020 presidential elections. Via Wikipedia.
Choropleth is a 20th-century coinage—more about that in a bit—but the first choropleth map was created more than a century earlier, by Baron Pierre Charles François Dupin (1784–1873), a French mathematician, engineer, and economist. Searching for a way to show how education levels correlated with prosperity, Dupin created a “Carte figurative de l’instruction populaire de la France,” in which light areas signified enlightenment and dark areas ignorance.
It took an American geographer and aficionado of Ancient Greek, John Kirtland Wright (1891–1969), to coin the term, in 1938, by which Dupin-style maps are now known. But Wright “cautioned against the use of choropleth maps,” notes his Wikipedia entry, “instead espousing the virtues of the dasymetric map,” which is basically a subcategory of choropleth map that adds symbols to further refine the information.
Choropleth may be MIA in the big dictionaries, but it’s all over Twitter. I even found a “data and analysis enthusiast” whose Twitter handle is @choropleth.
One of my beefs with these maps (it’s a problem with choropleth maps in general) is that the scale gets mentally overstated. Like the difference between 48% and 36% vaxxed is important, but just glancing at it most ppl probably the the range is much larger. https://t.co/lQdjAQzvtR— Sean T at RCP (@SeanTrende) May 21, 2021
New feature! You can now add place labels –such as cities, regions and countries– to Datawrapper choropleth and symbol maps. This feature will help your readers to orient themselves on the map .— Datawrapper (@Datawrapper) May 19, 2021
Visit our blog to learn how to use it: https://t.co/TE4ghWAzlx
In this week's Storytelling With Data class we were given the task "declutter and focus". I decided to use @observablehq to do a makeover of a choropleth map on internet access in the U.S. and walk through what the takeaways are. Think it came out nicely:https://t.co/1ULjJ9VKio
— Chris Henrick (@chrislhenrick) May 17, 2021
And here’s a fun etymological connection, via Haggard Hawks (Paul Anthony Jones).
Oooooh neat. I just looked up the word "choropleth" and assume the "chor" here is the same root...— On choisit pas (@maisonsubit) May 21, 2021