Half the country is within a quarter mile of a road
Twenty-one miles only means something against what is normal, and what is normal is that there is a road right there. Measured across all 340 million land cells of the lower 48:
| Distance to the nearest… | road | road or track | road or trail |
|---|---|---|---|
| median | 0.26 mi | 0.19 mi | 0.13 mi |
| share within ¼ mile | 49.9% | 62.5% | 64.3% |
| share within 1 mile | 81.3% | 92.8% | 94.8% |
| share within 5 miles | 97.97% | 99.40% | 99.88% |
| share within 10 miles | 99.72% | 99.89% | 99.98% |
| beyond 20 miles | 0.0039% | 0.0011% | 0.0003% |
Four thousandths of one percent of the lower 48 lies more than twenty miles from a road: about 118 square miles out of three and a half million, an area smaller than Detroit, scattered over the handful of places you can count on the map above. That is the whole subject here. It is a map of an almost empty set.
What this map calls remoteness
The straight-line distance from a point of land to the nearest mapped road. Nothing more than that.
Said precisely: distance as a compass reads it, not as you would walk it. A point a mile from a road across a cliff and a river counts the same as a point a mile across a meadow. Every road counts, whoever owns it — a gated ranch two-track, a forest road under six feet of snow, and an interstate are all roads. So is a road in Canada or Mexico; the question is how far the nearest road is, not the nearest American one.
It is measured on a 150 m grid in an equal-area projection, so a cell in Maine is the same size as a cell in Arizona and nothing needs correcting for latitude. Land means Census state polygons trimmed to the coastline, minus inland water — lakes are not land, and neither is the sea.
And what it is not
It is not a measure of how hard a place is to reach. It knows nothing about terrain, rivers, snow, gates, ownership, or whether a road is passable in anything less than a truck. It does not know about boats either: a shoreline scores whatever its distance to a road says, even where a skiff could be there in twenty minutes.
That last one changes the answer, so the ranked spots default to inland — only places where the surrounding circle is at least 90% land. Switch the panel to all US land and the leaderboard becomes barrier islands and mangrove coast, which is correct arithmetic and a worse answer to the question anyone is actually asking.
Whether a two-track is a road decides almost everything
OpenStreetMap tags a lot of the West as track: ranch roads,
logging spurs, mining two-tracks, things that are drivable but unbuilt. Count
them or don’t, and the same cell can move fifteen miles.
| Place | Roads only | With tracks | Change |
|---|---|---|---|
| The Thorofare, WY | 21.64 | 21.64 | 0.00 |
| Bob Marshall, MT | 18.19 | 18.10 | −0.09 |
| Owyhee Desert, NV | 19.38 | 0.42 | −18.96 |
| Desert NWR, NV | 17.10 | 0.73 | −16.37 |
| Frank Church, ID | 17.81 | 2.25 | −15.55 |
| Steens country, OR | 15.82 | 0.88 | −14.94 |
| Cabeza Prieta, AZ | 16.05 | 3.86 | −12.19 |
Every desert contender collapses under four miles. The two that hold are designated Wilderness and national park backcountry, where a drivable track legally cannot exist. The Thorofare and the Bob Marshall do not top the with-tracks list by being further from a road. They top it by being the only large roadless blocks with nothing drivable inside them at all.
So the two road maps answer different questions. Without tracks: where is the biggest roadless country? Mostly desert. With tracks: where is there no vehicle route of any kind? Almost entirely Wilderness.
Trails are a third map again
Add footpaths and the picture inverts. The Thorofare is 0.29 miles from the Thorofare Trail, which runs straight through it — the reason you can get so far from a road there is that people have been walking in for a century. The furthest you can get from a road or a trail is the Great Salt Lake Desert at 14.24 miles, and nowhere in the Rockies comes close. The question stops being where there is no road and becomes where there is no reason to walk.
How it was made
Roads and trails come from Overture Maps (OpenStreetMap lineage) plus the Forest Service’s national trail layer. Every road and trail is burned onto the grid and the distance to the nearest one is computed exactly, for all 601 million cells of the lower 48, by Euclidean distance transform.
The country is too big to do in one piece, so it runs in 24 tiles, each carrying a 60 km halo of surrounding country so that a cell near a tile edge still sees the roads just outside it. Each tile then proves its own answer: if the furthest cell in it is closer than the halo is wide, no road outside the window could have been nearer, and the number is exact. One coastal tile could not prove itself at 60 km and was recomputed at 120.
Checked against three answers worked out independently beforehand: Wyoming 21.64 miles, New York 3.65 miles to a road or trail, and New York’s land area to within 41 km² of the Census figure. Splitting the country differently changes no cell at all.