So I can't I believe I didn't catch this at first, but in #101 of The Annotated My Trip To NYC, Bill Luoma says, "These [paragraphs] are all slides by the way, slides that you would show to relatives after you get back from a trip." (I can't find a paragraph symbol on this keyboard, which is what Luoma uses.)

I had always sensed a pictorial quality in the paragraphs, but not in the imagist sense. Take this sentence for a instance, from 12 Peanuts & an Easton: "They wore regular clothes except for open windbreakers whose front said alternately POL & ICE." So there's a pleasent surprise in reading this of looking at 'POL & ICE' on the page, and visualizing it in the mind. It's a little thing, of course. But one thing that makes Works & Days so endlessly 'readable' is that it's a visual work, as well as a narrative one. Another instance is the Krispy Kreme symbol appearing next to the part where the narrator is describing the best way to eat Krispy Kreme donuts. But a key word in the first-quoted sentence from TAMTTNYC would seem to be 'show'. There's a passivity and a removedness, as in a narrator who says, I want to show you this. And as pleasant as being in a room with a person who wants to show you things, slides from a trip, for instance. Kerouac also writes alot about his prosody, but what keeps it from being a smothering venture for the reader, is that one doesn't the get sense of being told what something means. Same here, I think. I'm still hung up on that old show don't tell chestnut, from English Classes going back farther than I remember. (Mr. Lewis?) But it rings true.