Data Dive · Rung 3 · What's Related · 3.5

A choropleth spends its ink on land

And land does not breathe.

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The map everyone draws

Air quality by California county

Median air quality index by California county, 2024the twenty-two most populous counties - US EPA AirDatamedian AQIcountymedian AQI43.5870Los AngelesSan DiegoOrangeRiversideSan BernardinoSanta ClaraAlamedaSacramentoContra CostaFresnoKernVenturaSan FranciscoSan JoaquinSan MateoStanislausSonomaTulareSolanoSanta BarbaraMontereyPlacer

Median AQI, 2024, the 22 most populous counties

Now imagine it as a shaded map of the state, which is how this is almost always drawn.

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What that map is actually about

Half the ink, one twentieth of the people

45.7%
of California's land, held by its 29 least populous counties
4.9%
of its people
4.9x
San Bernardino's ink versus Los Angeles

San Bernardino County is 20,068 square miles against Los Angeles County's 4,060, and holds 23% of its population. On a shaded map it is the loudest thing on the screen.

The three questions
  1. What is this map giving its space to?
  2. Which counties dominate the shaded version, and which dominate a version sized by population?
  3. Which would you send to somebody deciding where to put a monitor?
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After the dive

The shapes on this page, in the library’s own words

the choropleth map

Which areas have more of this. Colour intensity by region.

What it leaves outBig areas shout. A large empty region looks more important than a small crowded one.
the bar

Bar length is the value, so it only means anything measured from zero. Start the axis anywhere else and the lengths stop matching the numbers.

What it leaves outOrder is a choice. Sorted by size it is a ranking; sorted by name it is a lookup; and the same bars say different things in each.

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