Midnight, 75 miles off the coast of Brooklyn, in that nameless bight between Cape May and Montauk: All that wasted light rising up from the city looms solid orange on the horizon. The water is deep--300 feet right here over the Hudson Canyon--and, in late spring, still heart-stoppingly cold. The boat, a sailboat with the usual top-hamper, gorgeous swages, cable and chain, a thick hull, is just a big tool, a place to direct instinct between wind and waves to get out to see this: black water, breaking white, some stars, and that mark of encroaching civilization in the distance. It's a wilderness when the land drops away. Or, it should be a wilderness. Coming out here to explore (not chasing fish, hauling oil: working) you want it to be a wilderness--off the grid, out of sight. It's something else when you know exactly where you are.

I've always thought that a sense of direction, a love of maps, evolves in proportion to one's fear of getting lost. By that measure, I am ter-rified. But without the risk, the chance to lose your way, is the ocean the same escape? A week before we set off, on a delivery from Annapolis to Maine, the federal government, in its benefi-cence, unscrambled the signals from its constel-lation of Global Positioning System satellites, the most recent wonders to replace Venus, Zubenel-genubi, and the Jovian moons as points of reference for the offshore navigator. Since it went online in 1995, GPS has been downgraded for all but the U.S. military; it was thought that the former rogue states, themselves now downgraded to "states of concern," would use the thing to aim their missiles. Civilians could use the technology, but only with built-in imprecision: Comparing time codes broadcast from 24 low-orbit satellites, the system would locate you reliably within a circle of a few hundred feet; after the signal upgrade, our GPS, a little hand-held no bigger than a Game Boy, was reporting 20 feet, 14 feet, 12. The margin of error is now smaller than the boat itself. You are here.

It changes everything; each point on or above the surface of the planet assumes a specific value in the GPS grid, as if one day, by fiat, all the far corners of the earth were given names. The grid itself--concentric rings of latitude and slicing meridians, converging at the poles--is not new. But there has never before been a way to locate yourself on it with such user-friendly ease--without parsing the static of a radio direction finder or puzzling with a loran, without shouldering a sextant, consulting a peevish chronometer and charting the approximate spherical triangle in which your position likely falls. Don't forget to account for parallax error, prismatic error, side error, index error, personal error: any one could put you miles off. Of course, you are also tracking your progress by dead reckoning between loose fixes, counting the miles passed on a given heading, or--to take it back another century or five--watching the birds, weighing the color of the water, tasting the muck brought up from the bottom on a tallow-dipped leadline. Gray seas, lots of weeds, bitter shells: this must be Georges Bank.

It's an urban paradigm, the snap-to grid, and on the water it has urban effects: shrinking and taming and warping virgin space. In Manhattan, home of the grid, even if you've never been to 33rd and Third you know where it is. It's at 33rd and Third. Those coordinates long ago replaced a string of dead-reckoning directions: Go up the Boston road, through the marshes, until you see a field near the hill past the last stand of elm on Kip's farm. Bring your transit, some stakes, and a street sign. (We all know the land did not survive its christening.)

Strangely, just as the seas (and the sky and those other deserts) are at last succumbing to our civilizing designs, we are losing track of the suburbs. In sprawl conditions, it's back to seat-of-the-pants navigation. To get to a movie theater in Tysons Cor-ner, Virginia--the capital of aimless neutrality--I was given the following directions: Take the feeder road around past the big mall to the Bennigan's. Go in there and work your way through the parking lot. It's down on the left, next to the Toys "R" Us, under a garage. Street names? Street numbers? Streets? It's a new wilderness of interpretive way-finding out there.

But for your next trip to the courthouse--through the light by the Wawa, under the overpass, be-hind Fuddruckers--it's GPS to the rescue again. Devices that merge position information with digital maps are cheap, easy to use, and right there mounted on your dash. On board the good ship Rancocas, GPS had this mapping feature that contained charts of the entire western hemisphere, from Cape Horn on up, every buoy and lighthouse set against a ragged liquid-crystal coastline. There was even a little "X" to mark our lonely progress through the matrix. One member of the crew spent the trip with his nose so close to the screen that he missed the seals and the sunsets, though not the seasickness. Look! It's all in here. It's all in here.

And it was: the near-gale gusts, the creeping shoals, the tankers in the night lit like Newark. It was all in there with the ranges and the bearings, the long waypoint lists, the false confidence, ETA revising every second. There was nothing between us and the abyss but plastic, double-A batteries, and unknown magic.

When the sun came up, we lost the loom of the city, but the ocean was marked in other ways. Every few minutes, all day, we sailed past a silver-foil balloon, losing its helium, floating on the water. They looked like Portuguese men-of-war, with shining bladders on the surface and colored ribbons trailing. We could see them within maybe 50 yards of our track, and we counted dozens. There must have been 100,000 more, each fixing a new intersection on the urbanized sea.