What can make Big Sur seem tricky to classify is the fact that it's a fictional novel, but based on the real events of a six week period in Kerouac's life, and the real people who surround him. This combination means we're dealing with a Roman à clef; technically fiction, but also thinly veiled autobiography. Kerouac makes no attempt to hide the fact that he's writing about what really happened. In fact, his introductory Author's Note (see "What's Up With the Epigraph?") reminds us to keep this in mind as we read. He explicitly refers to his other works and the part that the characters in Big Sur played in them. You'll see many passages like this one:
I can see Dave Wain really loves him at once, and Stanley Popovich too who's come along on this trip just to meet the fabled "Dean Moriarty" – The name I give Cody in "On the Road." (13.2)
Kerouac's not trying to play any clever, meta-fictional games, nor raise questions about the "fourth wall" – he's just being honest. This is a real account of what happened.
That being said, we can't forget that Big Sur is a work of literary fiction. This means that while the events and people are real, Jack can apply an authorial hand to their rendering. What does this mean? Big Sur has the structure and technique of a real novel, and it shows off brilliant literary prowess on Kerouac's part.
For an example, take a look at Chapter One. This chapter is a reflection of real events. Kerouac did wake up drunk and alone in a hotel room in San Francisco. But look at how the first chapter is structured and written. First sentence: "The church is blowing a sad windblown 'Kathleen on the bells'" (1.1). The first words of the narrative are "the church." Do you think spirituality is going to be important in this novel? The song being played is a sad one. Does this perhaps introduce the novel's tone? Now look at the last few lines of Chapter One. Jack hears "the lachrymose cries of a Salvation Army meeting on the corner below, 'Satan is the cause of your alcoholism, Satan is the cause of your immorality'" (1.1) We started with "sad," we end with "lachrymose." We start with the church; we end with Satan. Jack's already hearing accusations of alcoholism and feeling the pangs of Catholic guilt over his destructive habit.
And we've only looked at three lines in detail so far. There is a huge amount of detail packed into the literary rendering of these real-life events. It would be a mistake to assume that because the novel is autobiographical, it can't be literary, or to claim as Truman Capote did, that Kerouac's prose is typing and not writing. Because the novel is technically fiction, Kerouac has the freedom to mold certain details to meet his literary needs. The full moon, for example, fell on the night of September 5th in 1960; Jack writes that it falls on September 3rd, perhaps because the presence of a full moon is the ideal eerie setting for a night of delirium. If you want more examples, try tracing specific images or "signposts" throughout the novel. Start with the flying saucer or the bat overhead in Monsanto's cabin. These are all the result of deliberate structuring; the prose may be grammatically without form, but such fluidity isn't at the expense of the novel's good form.