The index combines "six measures of climate, topography, and water area that reflect environmental qualities most people prefer." Those qualities, according to the U.S. Department of Agriculture, include mild, sunny winters, temperate summers, low humidity, topographic variation, and access to a body of water.
These "natural aspects of attractiveness," as the USDA describes them, are intended to be constant and relatively immutable. They're not expected to change much over time, so the USDA hasn't updated its data beyond the initial 1999 scoring. "Natural amenities pertain to the physical rather than the social or economic environment," the USDA writes. Things like plants, animals or the human environment are excluded by definition. "We can measure the basic ingredients, not how these ingredients have been shaped by nature and man." I stumbled on these numbers after reading about a recent study linking natural amenities to religiosity. (U.S. counties with nicer weather and surroundings tend to have less religious residents.)
I've mapped all the counties above according to where they rank on the natural amenities index -- mouse over to check out how desirable (or not) your own county is. You'll see that Sun Belt counties fare pretty well -- especially ones in California and Colorado. In fact, every single one of the 10 highest-ranked counties is located in California. After Ventura County, Humboldt, Santa Barbara, Mendocino and Del Norte counties round out the top five.
By contrast, the Great Lakes region fares poorly, with most of the lowest rankings clustered around the Minnesota/North Dakota border region -- hey there, Fargo! The absolute worst place to live in America is (drumroll please) ... Red Lake County, Minn. (claim to fame: "It is the only landlocked county in the United States that is surrounded by just two neighboring counties," according to the county Web site).
And sorry, Alaska and Hawaii residents -- the USDA didn't have some of the data for your states (a common problem), so you're left out of the rankings. It's probably for the best, since Hawaii would probably have swept the top of the rankings, what with it being an island paradise and all.
For a sense of what contributes to these rankings, check out the maps below of the individual measures comprising the index -- darker counties rate as less desirable on these measures, while lighter ones rate higher.
Now, if you spend even a few minutes with the map above you can probably find a few things to quibble with in the methodology. If you hate summer, like me, it may seem that there's an inordinate emphasis on warm weather and ample sunshine. How else to explain that Inyo County, Calif. -- home to Death Valley, a place so inhospitable to human life that it literally has death in its name -- ranks so much higher than, say, the bucolic rolling hillsides of New England?
Or that Maricopa County, Ariz. -- home to Phoenix, a place that feels like the inside of a hot car for half the year -- ranks higher than Iowa's stunningly beautiful and criminally underappreciated Loess Hills region? Or that Washington D.C. -- home of sweltering summers, miserable winters, swampy humidity and little natural beauty to speak of -- ranks higher than any place at all?
On the other hand, it turns out that this index correlates well with a lot of human behaviors that researchers and politicians are constantly trying to understand better. For instance, the USDA's original report on the natural amenities index found that these measures "drive rural population change." The USDA found that rural areas with a lot of natural amenities saw the greatest population change between 1970 and 1996.
"The relationship is quite strong," the study found. "Counties with extremely low scores on the scale tended to lose population over the 1970-96 period, while counties with extremely high scores tended to double their populations over the period."
More recent research has found a relationship between natural beauty and religious attendance -- places with more natural amenities tend to have lower rates of religious adherence, according to a 2015 Baylor University study. Why go to church if you can hit the beach or the trailhead?
Of course, correlation isn't necessarily causation, and it would be easy to overemphasize the importance of natural amenities in the decisions Americans make about their lives. Still, the rankings provide plenty of food for thought. And the natural landscape is certainly one piece in the giant puzzle that explains why Americans do the things they do in their lives.
UPDATE: This post was updated with an explanation for why Alaska and Hawaii are not included in the rankings.
CORRECTION: A previous version of this post incorrectly left "County" uncapitalized in "Red Lake County." This was inadvertent and not intended as a slight to the great state of Minnesota. Special thanks to the residents of "Indignant Minnesota Twitter" who brought the issue to the author's attention via a change.org petition.