ON A WARM DAY in March 2011, I find myself in the back seat of a white, government-issue Chevy Suburban, rolling over spongy pasturelands in the sparsely populated foothills of the Ozark Mountains of southern Missouri. The vehicle is being piloted by Brian Ward, a geodetic advisor for the National Oceanic and Atmospheric Administration. Dave Doyle, the chief surveyor with NOAA’s National Geodetic Survey division, sits in the passenger seat, looking intently at a dashboard-mounted GPS screen. “Almost there. Just a little farther on,” Doyle mutters as Ward slaloms through an agitated herd of beef cattle.

We are aimed at the mean population center — or centroid — of the United States, a hypothetical and highly mathematical point calculated every ten years as part of the decennial census. According to the U.S. Census Bureau, the population center is “the place where an imaginary, flat, weightless and rigid map of the United States would balance perfectly if all 308,745,538 residents counted in the 2010 Census were of identical weight.” Picture that if you can.

“Looks like we continue on and then veer left,” says Doyle, a gregarious man with a mane of salt-and-pepper hair, glasses resting precariously at the tip of his nose. The edge of the pasture gives way to a stand of leafless hickories and dogwoods covered in white blooms. Due to the unusually warm weather, the small, four-petaled flowers have emerged a few weeks earlier than usual.

Our progress blocked by a high fence, we hop out of the truck and assemble. Before setting out into the woods, I punch the following coordinates into my hand-held GPS unit: 37°31´03˝ N, 92°10´23˝ W. From a manila folder, Doyle produces a satellite image of the area. A small digital thumbtack denoting the center pokes into a stand of trees on the opposite side of a small stream — the only barrier between us and the balance point of the American population.

SINCE THE FIRST DECENNIAL CENSUS in 1790, the center of population has moved roughly 870 miles southwest, from a point near Baltimore to a tiny hamlet in central Missouri at the fringe of the Mark Twain National Forest. The movement of the center is driven by regional population growth. It’s pushed and pulled by a kind of urban magnetism: the larger the population of a city or town, the greater the tug.

To trace the path of the centroid is to skim a great narrative spanning 220 years. That narrative is the nation’s history of growth, with each point along the way emerging as a sort of chapter: the rise of industrialism in the Northeast, the expansion of the western frontier, the waves of European, Latin American, and Asian immigration, the post–World War II population boom.

In its migration, only twice has the center of population come to rest in an actual population center: Baltimore, Maryland (population center, 1800), and Covington, Kentucky (population center, 1880, and hometown of a fourth-grade-dropout named Haven Gillespie, who penned numerous classic American songs including “Drifting and Dreaming” and “Santa Claus Is Coming to Town”). Over the years, the centroid has been found in places like Clarksburg, West Virginia, population center of 1840, where today the FBI operates its National Instant Criminal Background Check System to screen purchasers of firearms. Its path also passes through Portsmouth, Ohio, childhood home of Roy Rogers, which held the distinction in 1870. Portsmouth lost its NFL team to Detroit in 1933, its steel mills in the 1980s, and more than half its population of forty thousand between 1950 and 2000. And let us not forget Olney, Illinois, which held the honor in 1950. Hemmed in between industrial-scale farms, the town of ninety-one hundred is perhaps best known for its population of indigenous albino squirrels (penalty $500 for running one over), whose habitat is restricted almost entirely to a single city park.

A great series of advances and contractions, the movement of the American population has been diffuse and complex, a mass peopling counteracted by catastrophic bouts of depopulation. It’s difficult to imagine that a single measure could ever come close to summarizing the process, let alone reduce it to a single, floating point. And yet, here you have it.

In 1790, the first decennial census plotted the center of population in Kent County, Maryland, some twenty-three miles east of Baltimore. It was just two years after the ratification of the Constitution, and the U.S. population was concentrated along the Eastern Seaboard in the port cities of Boston, New York, Baltimore, and Charleston. New York, with a population of a little more than thirty-three thousand, was the nation’s largest city — and has remained so ever since. It’s hard to imagine, however, that Marblehead — today a quaint and touristic village a half-hour north of Boston — was then the nation’s tenth largest city, with a population of just under six thousand.

For the next hundred years, the centroid moved steadily westward, oscillating between the thirty-eighth and thirty-ninth parallels, over the Appalachian highlands of West Virginia and into the rolling pasturelands of southern Ohio and Indiana. As the population fanned west, further weighting the lands on the nation’s left half, the center was duly lured in its wake. Some sought economic opportunity or self-reinvention in western cities. Some went in search of gold in the Sierra or silver in the Rockies. Others were motivated by the promise of land and self-determination in giveaways such as the 1862 Homestead Act. These new migrants were granted 160-acre parcels (later increased to 320 acres in the “enlarged” Homestead Act of 1909) west of the Mississippi River. Many, however, found themselves suddenly thrust into a life of toil and servitude to the land itself as they clawed out a living from the arid and soon to be denuded reaches of the Great Plains west of the hundredth meridian.

Between 1910 and 1930, the center did something it had never done before or since. It remained virtually still. It’s not that population ceased to grow or that it stopped expanding. But the steady westward migration was counteracted by the mass immigration of millions of Europeans to the East Coast between 1890 and 1930, spurring draconian immigration laws such as the National Origins Act.

By 1930, the center was on the move again. But instead of continuing on its decisive westerly path it bent southward. That deflection, a trend that has continued to the present, was touched off by the great Texas oil booms, the rise of manufacturing in southern states, New Deal infrastructure projects including the great water-storage and hydroelectric projects of the Tennessee Valley Authority and Bureau of Reclamation, and the construction of permanent military bases in the South and West during and after World War II.

But arguably, the most influential factor in this change of course is air conditioning. That the centroid is headed, of all directions, southward, is a testament to our ability to blithely overpower climate with the brute force of fossil fuel. According to the 2010 Census, the Sunbelt cities of Los Angeles, Houston, Phoenix, San Diego, San Antonio, and Dallas now comprise six of the country’s ten largest cities. Over the last decade, the population of southern states has increased by around 14 percent, the fastest growth of any region in the country, outpacing the national growth rate of nearly 10 percent.

In the same period, Americans have abandoned the farm and village for the urban tarmac and suburban lawn. Industrialized agriculture and its attendant degradation of soils and depletion of ancient aquifers have triggered a steady exodus from the Great Plains. The emptying has wracked not merely Plains communities but all of rural America. In 1900, the United States was 60 percent rural; today it is 19 percent. Many counties that once lay along the edge of the frontier have been extensively depopulated and now hover near, or even below, their prefrontier population levels.

WITH A DAY TO SPARE before meeting Doyle and his group of centroid-chasing geodesists, I head east through tentacles of tract homes and onto a table-flat grid of farms and fields to the town of Centralia, Illinois — population center of 1960 (38°35´58˝ N, 89°12´35˝ W). Established in 1853 at the intersection of the two main branches of the Illinois Central Railroad, Centralia is today a place of sprawling parks and faded farms, of sturdy brick homes, whitewashed wood bungalows, and trailers in colorful states of disrepair. In the northern reaches of town, on East Rexford Street, men in slacks and ties and women in floral print dresses mingle in the street outside the New Covenant Church, which inhabits a weathered steel Quonset hut.

In the town center, the stone pillar of the Centralia Carillon — a 160-foot-high bell tower — reaches toward the blue sky, looming over the low buildings and the ubiquitous flashing arrow billboards, many of which bear the phrase GO ORPHANS. The Orphans, I soon learn, are the local boys, high school basketball team, which has just advanced to the state tournament. (According to a sign at the edge of town, the Orphans are also “The Winningest Boys Basketball Team In The Nation.”)

On the outskirts of town, pump jacks plunge into fields beside a series of ponds, their surfaces rendered a luminous green by a film of eutrophic algae. The croaking of bullfrogs offers a faintly melodic counterpoint to the rhythmic clanging of metal and whirring of gears, and I’m tempted to leave my car parked on the side of the road and investigate the raspy calls, until I note a sign explaining that the marsh is actually part of a massive municipal sewage lagoon system.

Wandering Centralia’s hushed streets, I find resident Cindy Snyder outside St. Mary’s Catholic Church, speaking with three members of her congregation after Sunday services. I approach and explain my search for the plaque commemorating the 1960 center. Snyder says she knows of the designation but not where the marker is set. I show her some images I’ve gathered from a 1961 issue of Life magazine. One depicts a crowd assembled in a field holding placards with messages such as FRONT AND CENTER, CENTER OF ATTRACTION, and HEART OF THE U.S.A. emblazoned across them.

Snyder takes the images in hand, holding them close, squinting for small clues. “It’s hard to say,” she says. The weathered triangle of a wood barn and the stark white cylinder of a silo are the only defining features. Snyder says many surrounding plots like this have been built over with houses or bought up by large factory farms and the agribusiness goliath Monsanto, which operates a fortresslike facility south of town where its patented Roundup Ready soybeans are bagged and stored. It’s not just the family farms that have disappeared, Snyder says, but the small family-run businesses along Broadway, the town’s main drag, and even the young families themselves, who have gone in pursuit of jobs and larger, newer homes in the suburbs of St. Louis, Chicago, and Indianapolis.

Before leaving, I decide to visit the site of one of the town’s most significant and harrowing historic events: the No. 5 Coal Mine disaster of 1947 (not to be confused with the infamous coal mine fire in Centralia, Pennsylvania, remnants of which still burn today, fifty years later). On a March day, 142 miners descended 540 feet into the DuQuoin monocline, a formation rich in bituminous coal. On an average day, the men who worked the No. 5 seam hauled two thousand tons of coal up from the depths. Much of that coal was sent to the steel mills and automobile plants of the Midwest, fueling the manufacture of the Fords, Chevrolets, and Chryslers that carried the population out of the centers of cities, along the asphalt trails of new highways, and into tract housing developments in the nation’s rapidly expanding suburbs.

On March 25, however, something went terribly wrong at Centralia No. 5. Life magazine described it as a “soft, puffing explosion” deep underground. The fire began when tiny particles of coal dust ignited after an errant charge was detonated in the depths. Of the 142 miners who went down that day, 111 were killed by fire and “afterdamp,” toxic gases that remained in the depths after the explosion. Woody Guthrie’s song “The Dying Miner” memorializes the miners, and depicts their harrowing final moments:



My eyes are blinded with fumes,

But it sounds like the men are all gone,

’Cept Joe Valentini, Fred Gussler and George,

Trapped down in this hellhole of fire.

I found a small plaque commemorating the men of Centralia No. 5 in an empty city park in the neighboring town of Wamac, surrounded by brightly painted playground equipment and creaking pump jacks. I never did find the disc marking the 1960 center of population.

IN THIS AGE of geosynchronous satellites and fully integrated global positioning systems, Dave Doyle is accustomed to plotting positions with accuracies to the nearest centimeter. Having joined NOAA’s geodetic division in the early 1970s, he has either participated in or overseen these population center surveys since the 1980 Census. He was first introduced to the idea of the centroid when his boss and mentor handed him a large manila folder with the word centers hand-scrawled across it. “He was passing the torch on to me,” he says.

The folder is stuffed with an array of yellowing papers, many of which are letters from private citizens looking for midpoints of states, counties, and townships. “When I first saw this, I thought, What is going on here? Why do people care about any of this?” says Doyle. But in his thirty-plus years on the trail of the centroid, he has come to embrace the idea. “People want to know where they are on the surface of the earth,” he explains. “They want to know where they stand.”

For most of human history, centers have been the province of myth. Mircea Eliade, the late historian of religion at the University of Chicago and author of The Sacred and the Profane, charted a set of ancient centers. He called these axes mundi, or “world pillars.” The axis mundi, he wrote, “connects and supports heaven and earth,” while its base “is fixed in the world below.” David Adams Leeming, in his book Creation Myths of the World, notes that mountains, trees, stones, and other prominent natural landmarks often stand at these sacred midpoints. “Centers are always powerful,” wrote Boston University professor of religion and anthropology Frank J. Korom, “because they constitute a point of intersection between the three regions: heaven, earth, hell.”

Centers imply gravity, a force of social cohesion. The Great Oak of Southern California’s Luiseño tribe, for instance, marks their sacred center point and is believed to grow from the ashes of Wiyot, their ancestral hero. The sipapu, center of the Hopi people, is a travertine spring at the bottom of the Little Colorado River canyon where their ancestors are said to have emerged from underground into this world. The omphalos, the navel of the world, a beehive-shaped structure said to allow communication with the gods, sat at Delphi, the heart of the ancient Greek world, and served as a nexus between the natural and supernatural. The Irminsul, sacred center of the Saxons, is supposed to have been a pedestal or holy tree. Some historians have noted clear similarities between the Irminsul and the Yggdrasil, the great mythical ash of Norse mythology, whose roots were believed to anchor the earth to the heavens.

Once enshrined within a culture, the idea of a sacred center is difficult to erase. During Charlemagne’s eighth-century campaign to subdue and unify the tribes of Saxony and bring them under the rule of the Holy Roman Empire, one of his first decrees was to destroy the Irminsul. Nearly one thousand years later, during the great nineteenth-century revival of Germanic folklore, Jacob Grimm pinpointed the lost location of the Irminsul to “15 miles from the town of Obermarsberg in the Teutoburg Forest.”

Not surprisingly, maps have been critical in visualizing these sacred centers. The eighth-century Beatine Map (also known as the “T and O,” or orbis terrarium, map) is a simple plot that places Jerusalem at the axis of three continents — Asia, Africa, and Europe — and the center of the medieval world. And Jewish scripture says, “As the navel is set in the center of the human body, / So is Israel in the center of the world.”

But Israel itself is a land of multiple centers. The holy city of Jerusalem radiates outward from the Foundation Stone, with its sipapu-like aperture known among the faithful as the Well of Souls. The Samaritans, a Judaic sect, established their own holy center point at Mount Gerizim near the West Bank city of Nablus. Muslims plot their center within a center at the Grand Mosque at Mecca. Affixed to the Kaaba (the cube-shaped shrine believed by Muslims to be situated at the center of the world) is the holy Black Stone, itself set inside a circular hollow within an ornate silver frame.

These midpoints have remained sacrosanct — and in place — for centuries. But here in the United States, there is no omphalos, no Kaaba or Foundation Stone — there is only the open road unfurling. Our diverse population is busy moving, being born, and dying, changing careers and cities, pressing outward into the ever-expanding arms of suburbs and exurbs. The center never rests. Every time an elderly woman passes in Yuma, Arizona, or a child is born in Caribou, Maine, or a young couple pulls a U-Haul trailer onto a busy avenue in San Francisco, the axis shifts. Perhaps the author William Least Heat-Moon said it best when he told a crowd assembled in Lowell, Massachusetts, for the fiftieth anniversary of Jack Kerouac’s On the Road, “I’ve always thought that the fifty stars on the flag should be replaced with fifty tires.”

AT AN INTERSECTION flanked by wide fields, a cemetery, and a gas station, Doyle locates an oxidized metal disc glinting in a nondescript patch of grass. Before we set out to find the 2010 center, he has led our group into the tiny hamlet of Edgar Springs, population center of 2000 (37°41´49˝ N, 91°48´34˝ W), roughly 110 miles southwest of St. Louis.

As we revolve around the marker, snapping pictures and surveying the surroundings, a large man emerges onto the front porch of a small wood-frame house next to the marker. He waves hello, a crow call and whistle attached to a string around his neck. His name is Junior Harris, and he grew up in Edgar Springs, population two hundred and change. “May I help you gentlemen?” he asks in a rich Ozark drawl. Doyle asks if he knows about the marker. He nods. “If I walk to the east side of my property the whole world shifts,” says Harris with a chuckle.

While the tide of Manifest Destiny was anything but glacial, some in these small towns, like Harris, have retained an intimate relationship with the local geography and a sense of the land before it was altered by progress. Harris describes the surrounding tracts of farmland and rattles off the names of the people to whom they belong. He knows where the power lines cut over the rolling ridges and where the water and sewage mains run. He knows the swamps, the woodlands, the remnant swaths of elk grass — a hallmark species of the tallgrass prairie that once grew so high and thick that, Harris says, “two men standing two feet apart wouldn’t know that they were standing right next to each other.”

Harris also knows that the marker beside his home is a mere placeholder. (He’s willing to admit this even though the small benchmark earned him the title “Mr. Middle America” in a Financial Times article a few years back.) He points to the woods beyond his property and tells us that the “real” 2000 centroid is located out there, three miles east of the ceremonial marker, near the spring where half a century ago his grandfather used to drive his cattle during the hot Missouri summers.

The decision to place the marker in accessible places, such as Harris’s front yard, is a practical one, says Doyle. The Census Bureau and NOAA want to position the center markers accurately — but not with such precision that the general public must cross private property or brave ticks, thorns, and poison ivy to find them. Of course the center of population cannot be beholden to such rules. Like a free-drifting balloon, it comes to rest where it will.

DOYLE AND HIS colleagues agree that the centroid will move a little farther south and west, maybe even slipping out of Missouri and nudging into northern Arkansas. There he thinks it will soon come to rest — the axis of a population at last in equilibrium.

But such predictions may take one critical factor for granted: a stable climate. Like the speedometer needle of a vehicle with a stuck accelerator, average temperatures continue to climb. In the last century, average temperatures across the continental U.S. have jumped by roughly one and a half degrees Fahrenheit, and the rate of overall warming has more than tripled since 1970. Moreover, the top ten warmest twelve-month periods on record in the U.S. all took place between 1999 and the present. A 2009 study from the United States Global Change Research Program predicts that the average temperature in the continental U.S. will increase by between four and eleven degrees Fahrenheit by 2100. The southern states are projected to see the most fearsome warming, with the number of days per year above ninety degrees jumping from 60 today to 150 by the end of the century.

In addition to unprecedented warming, the South has seen the bulk of the nation’s damaging weather — from droughts and hurricanes to floods and tornadoes. To visualize this pattern, one can view a color-coded map published by NOAA showing where the majority of billion-plus-dollar disasters have occurred during the last thirty years. The striking feature is that the states of the Southeast — North Carolina, South Carolina, Georgia, Tennessee, Alabama, Mississippi, Louisiana, Arkansas, Oklahoma, and Texas — are all rendered in shades of deep red, denoting a kind of statistical bull’s-eye of severe weather events.

While debate continues about the connection between warming temperatures and storm activity, the extreme weather thunders on. In October 2012, the European insurance firm Munich Re released a report stating that extreme weather events in North America had almost quintupled in the period between 1980 and 2011. In total, there were fourteen billion-dollar weather events in 2011 alone, the most ever recorded in a single year in the U.S. One storm in April spawned 343 individual tornadoes. But the year’s most destructive storm came in May, when an EF5 tornado cut a furrow through the town of Joplin, Missouri (150 miles southwest of the 2010 centroid), reducing neighborhoods to rubble and killing at least 160 people. In 2012, there were more than ten billion-dollar events, including the year’s most devastating, Hurricane Sandy.

There is also the threat of crippling aridity. By the end of the summer of 2012, more than 65 percent of the country was found to be in a state of “moderate to exceptional” drought, the highest percentage ever recorded in a twelve-month period. In parts of New Mexico and Colorado, vast stands of pinyon and juniper — no strangers to heat and dryness — have been perishing from a lethal cocktail of high temperatures and thirst, mottling dry mesas rust and brown. Jonathan Overpeck, a geosciences professor at the University of Arizona and IPCC author, has suggested that there is better than a one in ten chance that the Southwest may experience a crippling “megadrought” by 2100, the sort of event that has visited the region at least three times in the last two thousand years. Such a scenario could result in mass tree die-offs, colossal fires (like those that burned over 9 million acres last year alone), and a significant decrease in snowpack and water delivered to the Colorado River, a key source of drinking water for 30 million Americans living in the West.

Meanwhile, the northern tropics appear to be advancing toward the pole — by as much as eight degrees, according to some researchers. A report released in 2012 by scientists from the University of California, Riverside, speculates that this expansion is fueled by emissions from the industrialized world — as well as by soot from forest fires and wood-burning stoves in developing countries — and may trigger a corresponding advance of subtropical deserts.

A shift of a few degrees in the edges of the Sonoran or Mojave could nudge cities now at the margins of habitability into the midst of unconquerable deserts. What might such a scenario hold for cities such as Phoenix, Tucson, San Antonio, El Paso, Albuquerque, Las Vegas, and San Diego, places made habitable by great water engineering projects now threatened by prolonged drought? The human fallout is hard to imagine. But the capitulation of a string of large, southern cities would doubtlessly have a marked effect on the centroid.

THE OZARK MOUNTAINS spread to the blue horizon like concentric ripples thrown from a droplet hitting still water. We’ve left Junior Harris’s front lawn in Edgar Springs and are pressing southward, winding over Highway 32 to Plato, Missouri (37°31´03˝ N, 92°10´23˝ W). A small village of 109 people (up from 74 in 2000), Plato lies roughly 175 miles southwest of St. Louis.

Upon arrival, the first duty of the team, made up of workers from NOAA, the Census Bureau, and the Missouri Division of Geology and Land Survey, is to scout a suitable place to fix the 2010 commemorative marker. In a town as small as Plato, the task is quickly accomplished. On a prior scouting trip, Doyle had found a small park near the center of town. The bulk of Plato’s businesses — a post office, a bank, a café, and a farm supply store — are visible from the proposed site. A nearby granite monument tells of the town’s founding in 1858. The name Plato, as several of us had wagered, was taken from the ancient Greek philosopher. (Mike Ratcliffe, a cultural and historical geographer with the Census department, jokes that in addition to being in the middle of Missouri we are also “at the center of The Republic.”)

A small group of locals begins to congregate as Doyle launches into an impromptu presentation about the calculation and demographic significance of the centroid. From a gray duffel, he retrieves the twelve-inch steel disc along with hand-drawn plans for the marker’s housing: a squat pillar of Missouri red marble. Doyle hands the thirty-pound marker to Bob Biram, village councilman and liaison for the upcoming ceremony. Biram, clad in a camouflage ball cap, grunts lightly as he takes the metal disc in hand, holding it edgewise against his belly to steady the weight. “That is pretty,” he says with a smile.

But Biram bears bad news. Though he agrees the park would be an ideal place for the marker, he can’t grant permission because the village does not own the land. The parcel, the footprint of a former pharmacy, remains in the estate of the Tilley family, which once owned and operated the store. Ms. Tilley died a few years ago, but Biram believes that some of her relatives remain in the area. He offers to make some calls.

While waiting, the party decides to take lunch at Weber’s Café, Plato’s lone eatery (which also doubles as its sole grocery store). Over heaping servings of chicken-fried steak and mashed potatoes, resident Barbara Pinkston asks Mike Ratcliffe about the precision of the count. Specifically, she wonders how the bureau knows with certainty that everyone has been included.

Ratcliffe explains the various protocols used by census takers to ensure an accurate count, including making repeat visits to households. “They are instructed to make six visits,” Ratcliffe explains. “After that, it becomes very expensive. So if they can’t get you in person, they’ll go to the neighbors to try to get a count of how many people live in your household.”

“But what if you just don’t want to be counted?” Pinkston asks. “Lots of folks around here get scared about the idea of a ‘head count.’ And they do whatever they can not to be found.”

Ratcliffe says that no matter how carefully the census is undertaken, there will always be uncertainties. He points out that the census is a “snapshot” in time, and that statistical estimates are used to help appraise the accuracy of the count. The bureau calculates a high, low, and middle figure based on different growth scenarios, he says. He explains that the count is then compared to these various statistical figures. “This year, it turned out that the number we got was very close to that middle figure,” says Ratcliffe. “That tells us that we were very accurate with our count.” With that, Pinkston seems satisfied.

But of course not everyone gets counted. While some citizens inevitably slip through the cracks, the centroid’s most serious limitation lies in its narrow definition of citizenship and legal residency and, by extension, its mathematical exclusion of anyone, past or present, who does not fit these narrow strictures. Between 1790 and 1850, not a single American Indian was tallied in the decennial census. Also uncounted were the tens of thousands of slaves who escaped the bondage of the plantation for northeastern cities before emancipation. Today there are an estimated 11 million undocumented (which is to say, uncounted) immigrants scattered across the country. Any talk of the centroid or its “advance” must be considered in light of these unaccounted-for populations.

When we finish lunch and emerge into the bright Missouri sun, Bob Biram has a smile on his face. He’s managed to make contact and is confident that the family will be happy to have the monument placed on their land. With the location nearly settled, we load up in the fleet of white Suburbans and trek to the “real” population center, which lies in the woods a few miles to the north.

We cross the edge of the cow pasture, ditch the vehicles, and head into the trees. The stream, Rock Creek, is only a few hundred feet ahead and a few inches deep. We wade across quickly, passing through a second dry streambed and into a thicket of blackberry bushes and small pines. After a few minutes, Doyle calls out for us to go slowly, then to stop. According to his GPS, we’ve arrived. Before us, in a small clearing, stands a thin, ragged hardwood sapling. As Doyle reaches to touch one of its leafless limbs, the group falls silent.

“This is it,” he says solemnly. “The center tree.”

Ratcliffe and Darrell Pratte, the director of the Missouri Land Survey Program, quickly gather a few pale chunks of limestone and construct a small cairn at the tree’s base. Here at the quantitative axis mundi, the nation’s population whirls around us like a great spiral galaxy or a hurricane about its eye. For a moment there is calm, quiet. The only sounds are wind in the treetops and water coursing lightly over stone.

And then someone laughs and the air of contemplation has passed. The center is restless, indefinable. It was no more “here” than where we’d been standing a few moments earlier, in the town of Plato. The census tells us the nation adds 227,000 people per month, a new Reno every thirty days. At that rate, another fifty-two people had entered the population in the few minutes we’d been standing under the scrawny tree at the nation’s momentary fulcrum.

The center was certainly not far away. Perhaps it was lingering in the next valley over, or languishing momentarily along the banks of Rock Creek. Maybe it was circling back in an eddy along the asphalt river of Highway 32. Maybe — but there was no point in thinking it would stop for us.