The author has selected four "empty spaces" in the United States, places where very few people live. He made his selection on the basis of nighttime satellite photos which showed dark areas of very few lights, unlike most of our well-lit country. The four areas he selected were northeastern Maine, next to the Canadian border, a part of western Pennsylvania, southeastern Oregon, and the high desert country of New Mexico.
Of course any area will have some people living there, as well as having had past inhabitants, and one reason he selected these four areas is that they have interesting pasts. Stark's approach is to visit these areas, describe what they feel like today, and then recount details of their past, all of which makes for a fascinating read.
In Maine, he takes his wife and two children by canoe down a river, the same river that Henry David Thoreau wrote about, not in WALDEN, but in his writings about the remote north woods of Maine which he visited three times int he l840's and 50's. He attempts to climb a rugged mountain peak, but turns back, as Thoreau did, because of bad weather, leading to his thoughts on how vulnerable humans are to nature and weather.
You'd normally not think of western Pennsylvania as a remote area, but the mountainous area Stark visits was initially logged off 100 years ago and lost most of it economic value. It was bought by the U.S. government and became federal forest land, explaining why it is mostly uninhabited today. But 300 years ago it was an strategic area, near key rivers, and was fought over by Britain and France in a the French and Indian war, which was crucial in determining the fate of North America. Interestingly, the young George Washington fought with the British in this area.
Southeastern Oregon, while remote, is full of natural life and attracted the attention of the famed naturalist, John Muir, who did much to preserve natural areas from destructive human encroachment. And it was important, too, as a desert that had to be crossed by wagon train immigrants to the Willamette Valley of Oregon, frequently with tragic losses. Today, Stark found mainly cattle ranchers who graze their stock on vast areas.
The last area that Stark visits is in New Mexico, an area that the Spaniards trekked through in the 1500's, seeking the fabled "seven cities of gold" which turned out to be illusory. It's rugged country, but again, he, his wife, and two children, hiked and camped in remote canyons, and he writes of Aldo Leopold's 20th century efforts to preserve this region by showing "the interrelatedness of the natural world and the all-too-common human ignorance of it."
Finally, are these blank spots of any real significance? Starks thinks so, and eloquently writes of the lessons that their wilderness imparts to us, "Creation is continuous and infinitely complex. Man is only the tiniest, tiniest part of all Creation. And you - yes, you - are even tinier than that. That's what the blank spaces tell us." And these blank spaces on earth are only part of the incredibly vaster spaces of the universe.