If you have an Internet connection, you’ve likely seen one of these maps of America, in which each state’s character is boiled down to a single predilection or predicament. The maps are undeniably entertaining: You check out the state you live in, the state your cousin lives in, the state you dislike for whatever reason, and then send it to a friend so she can do the same. Thanks to their shareability, the maps have quickly become a fixture of Facebook, Twitter, and websites (Slate among them) eager to profit from our fascination with federalism.
There’s nothing wrong with reading and sharing maps like this, of course—they’re fun and might even teach you some trivia. But the maps are often misleading. Crucial information can be left out, and patterns can emerge where there are none. The underlying data is usually noisier than it appears, and a small change in methodology can result in drastically different maps. If you understand the sensitivity of the data and the process used to create the map, this isn’t much of an issue. But when someone shares an amusing U.S. map on Facebook, how long do you usually spend reading the fine print about methodology? You might be surprised at what you’re missing.
Many different kinds of U.S. maps have gone viral in recent months. My focus here is on maps of the United States in which each state is given a single, non-numeric label, as these tend to be among the most widely shared. For instance, you may have seen the maps of popular baby names by year created by Reuben Fischer-Baum. In many instances, a single name surges in popularity in a given year, appears to take over the United States like a virus, and then fades away. The name Ashley, for example, appears to go from limited popularity in the 1980s to near ubiquity by the early ’90s.
Watch the maps in GIF form, and it’s impossible not to come away with the conclusion that American parents were in the grip of an Ashley-naming epidemic in the final years of George H. W. Bush’s presidency:
In 1984, only 13 states are labeled Ashley; by 1992, 30 states are. But it turns out that in 1984, a female baby born in the United States was actually 8 percent more likely to be named Ashley than in 1992.
Ashley was still the most popular girls’ name in 1991 and 1992. But its newfound dominance of the map is not the result of its growing popularity. Ashley was on the decline by the early ’90s—but other names were declining even faster. The original maps don’t actually say that Ashley was increasing in popularity in the early ’90s, but the way the information is presented, that misunderstanding is almost unavoidable.
Even within each individual name map, the results are not always as straightforward as they seem. In the 1992 map, Missouri is marked Jessica, while Iowa, its neighbor to the north, is marked Ashley. Glancing at the map quickly, you would likely assume that Ashley was therefore more popular in Iowa than in Missouri. But in 1992, 2.7 percent of all babies born in Missouri were named Ashley. This is a higher rate than in Iowa (2.3 percent) and indeed higher than the national average (2.4 percent). It just so happens that Jessica was even more popular in Missouri than Ashley.
Again, this doesn’t mean the baby-name maps are wrong. They don’t purport to show anything except the most commonly given name in each state. In fact, these particular maps are well-designed and informative, if you have time to wade through the implications of the data. But it’s easy to see false trends here. Behind each map is data for hundreds of names across 50 states that would need to be examined closely to find the real trends. Unfortunately, there is no such thing as a viral Excel sheet.
Even a carefully researched and explicated map can be lifted in JPEG form and distributed without proper context. A perfect example of this is the map below, created by Music Machinery blogger Paul Lamere. The map shows each state’s “Most Distinctive Band”:
Lamere’s concept was well thought out, and his original post took care to explain his process and to offer the appropriate caveats to his readers. The map was meant to illustrate something very specific: which band is more popular in a given state than in any other state. But when the map was republished, on sites including BuzzFeed, Time, and Slate, his notes disappeared, and, even worse, the map was given a new, misleading title. Now the map was being described as showing each state’s favorite band, period. Naturally, “Your State’s Favorite Band” is a more attractive and easier to understand headline than “Your State’s Most Distinctive Band.” If it wasn’t for Mother Jones taking other sites to task for this mislabeling, the error may have gone unnoticed. (Slate’s post on the map has since been corrected.)