It’s a good reminder of what people often forget about the 2016 election: “It was very close,” Field says. What you notice second is just how much purple there is everywhere else. What you notice first when you look at the map is that the solid red wall extending from North Dakota to Texas on the map Yingst shared is almost white in this rendering. Purples portray areas where one party or another won by a narrow margin. A light pink indicates a high Republican vote share in a sparsely populated area. A bright, vibrant blue indicates a high Democratic vote share in a densely populated area. Instead, it uses color to indicate the party’s vote share in each county, and opacity (in mapmaking, it’s called the “alpha channel,” hence, value-by-alpha) to indicate the population in a given area of the county. It doesn’t account for where votes were most likely cast within a county. The value-by-alpha map is similar to the dasymetric dot density map, and in some ways, even simpler. Presidential election 2016: Value-by-alpha Ken Field But on the dasymetric dot density map, it’s the blue that stands out, conveying the difference between the popular vote, which Clinton won, and the electoral college vote, which Trump won. But by completely coloring in all the counties, it gives counties where only a few hundred votes were cast the same visual weight as counties where hundreds of thousands of votes were cast. That map uses different shades of red and blue to indicate whether candidates won by a wide or slim margin. Taken together, Field says, these methods offer a far more detailed illustration of voter turnout than, say, the map in Yingst’s tweet. That’s to avoid placing lots of dots in, say, the middle of a forest, and to account for dense population in cities. Then, rather than distributing the dots evenly around a county, he distributes them proportionally according to where people actually live, based on the US government's National Land Cover Database. On this particular map from 2016, there are roughly 135 million dots. Instead of filling an entire state or county with the color red or blue to indicate which party won, Field uses red and blue dots to represent every vote that was cast. The term “dasymetric” refers to a map that accounts for population density in a given area. To Field, there's no such thing as a totally comprehensive map, but he says, "Some are more truthful than others." The so-called dasymetric dot density map is one of them. Presidential election 2016: dasymetric dot density Ken Field (Well, that and he just really loves maps.) That's one reason why Field recently published an extensive gallery of more than 30 alternative maps designed to tell markedly different stories about what happened on election night 2016. But focusing on that map alone could lead Republicans to overestimate their advantage, and lead Democrats to misunderstand the best ways to catch up. It stands to reason that President Trump would want that particular map hung in the West Wing. "It’s a question of the level of detail that people are interested in understanding." "People see maps of any type, and particularly election maps, as the result, the outcome, but there are so many different types of maps available that can portray results in shades of the truth," Field says. The problem is believing that any single map can ever tell the whole story. The problem, he says, isn't with people's partisan interpretation of the map. A self-proclaimed "cartonerd," Field is a product engineer at the mapping software company Esri and author of a guidebook for mapmakers called Cartography. In reality, both sides are right, says Ken Field.
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