Is this what you mean?

    let f = makeMap x y
    in map someFunc . filter other . map f $ userList

I suspect not as it certainly doesn't seem to improve the situation. Perhaps you could elaborate?

Edit to add: I was focused on the "write out the callback given to map using a let block" part and not the meaningful name part, but that's perhaps what's confusing about this to me, as (makeMap x y) seems like the most clear name possible here, what else could you do? This?

    let mapOfXy = makeMap x y
    in map someFunc . filter other . map mapOfXy $ userList

It only obscures things.