America in The Autobiography of Benjamin Franklin is unformed and exciting; it's not yet a country, but it's more than a random collection of colonies. It's a new civilization taking its first baby steps. The people who live in this America are eager and excited, brave and bold, and they're figuring out what kinds of rights they want and need. Actually, there are lots of things this America needs, and Franklin's in the position of helping to shape or provide most of them. His America's actually a lot like a thought-experiment, where people keep adding elements to a new civilization. We're just lucky that someone like Franklin is around in the 1700s to contribute so much to it, instead of people like, say, Attila the Hun or the Three Stooges.
The Autobiography reveals an exciting America, a place where anything can happen and any idea can be achieved. In other words, Franklin's narrative shows us the American dream in action.
Franklin's narrative doesn't tell us as much about the Philadelphia he lives in as it does about the Philadelphia he wants it to be. He's more invested in shaping the city to his own template than he is in explaining what its present looks like.