I felt as if I were in a computer museum, watching the curator take his favorite oddity for a spin. McPhee has never used a traditional word processor in his life. He is one of the world’s few remaining users of a program called Kedit, which he writes about, at great length, in “Draft No. 4.” Kedit was created in the 1980s and then tailored, by a friendly Princeton programmer, to fit McPhee’s elaborate writing process.

The process is hellacious. McPhee gathers every single scrap of reporting on a given project — every interview, description, stray thought and research tidbit — and types all of it into his computer. He studies that data and comes up with organizing categories: themes, set pieces, characters and so on. Each category is assigned a code. To find the structure of a piece, McPhee makes an index card for each of his codes, sets them on a large table and arranges and rearranges the cards until the sequence seems right. Then he works back through his mass of assembled data, labeling each piece with the relevant code. On the computer, a program called “Structur” arranges these scraps into organized batches, and McPhee then works sequentially, batch by batch, converting all of it into prose. (In the old days, McPhee would manually type out his notes, photocopy them, cut up everything with scissors, and sort it all into coded envelopes. His first computer, he says, was “a five-thousand-dollar pair of scissors.”)

Every writer does some version of this: gathering, assessing, sorting, writing. But McPhee takes it to an almost-superhuman extreme. “If this sounds mechanical,” McPhee writes of his method, “its effect was absolutely the reverse. If the contents of the seventh folder were before me, the contents of twenty-nine other folders were out of sight. Every organizational aspect was behind me. The procedure eliminated nearly all distraction and concentrated just the material I had to deal with in a given day or week. It painted me into a corner, yes, but in doing so it freed me to write.”

McPhee’s next book, “The Patch,” will be a collection of previously uncollected work reaching all the way back to his first magazine job, starting in the late 1950s, when he wrote celebrity profiles for Time magazine — often without actually meeting the celebrity. (“He looked like a big basset hound who had just eaten W.C. Fields,” he wrote about Jackie Gleason.) If that sounds straightforward, McPhee has decided to make it not so. He has turned it into another structural challenge. “The Patch” will gather fragments of the old work, arranged by McPhee into a pattern that pleases him, out of order, like patches in a quilt. (“I’m still trying to get my head around it,” Alex Star, McPhee’s current editor at Farrar, Straus and Giroux, told me.)

The title piece of “The Patch” is a short essay that McPhee wrote about the death of his father. It is, in its way, as revealing as anything he has ever written. Fishing, McPhee writes, was his father’s “best way of being close.” In the essay, he finds himself alone in a hospital room with his father, who has suffered a debilitating stroke. McPhee doesn’t know what to do, and so he begins, spontaneously, to talk about fish, particularly a species that he had recently been out catching in New Hampshire: the aggressively ravenous pickerel. “Pickerel that have been found in the stomachs of pickerel,” McPhee writes, “have in turn contained pickerel in their stomachs.”

I went on in this manner, impulsively blurting out everything I could think of about the species, now and again making comparisons and asking him questions — did he remember the sand sharks off Sias Point? the rainbows of Ripton? the bullhead he gutted beside Stony Brook that flipped out of his hand and, completely gutless, swam away? — to which I expected no answers, and got none.

It is a touching scene of laconic masculine love — emotion expressed not directly but through the medium of shared wilderness activities. After which McPhee does something structurally magical. There is a section break, some white space, and then a paragraph of fish facts that, in the context of his father’s impending death, reads like a prose poem:

With those minutely oscillating fins, a pickerel treads water in much the way that a hummingbird treads air. If the pickerel bursts forth to go after prey, it returns to the place it started from, with or without the prey. If a pickerel swirls for your fly and misses, it goes back to the exact spot from which it struck. You can return half an hour later and it will be there. You can return at the end of the day and it will be there. You can go back next year and it will be there.

McPhee’s great theme has always been conservation, in the widest possible sense of the word: the endless tension between presence and absence, staying and leaving, existence and the void. It is, of course, a losing battle. Our fathers will die. The Pine Barrens will contract. Civilization will continue to invade the vast wilderness of Alaska. The course of the Mississippi River once roamed erratically “like a pianist playing with one hand,” but humans put a stop to that. Developers want to mine mountains, pave islands and turn the Grand Canyon into a lake. North America, in McPhee’s telling, is the product of nearly infinite vanished worlds, with species and climates and mountain chains and oceans all lost in the chasms of deep time — so far gone that even the most brilliant geologists are unable to extrapolate all the way back to their original bubbling source.