Blowing Smoke: Don doesn’t have cab fare to get home from Midge’s. She tells him to walk across the park, meaning Washington Square Park. He’s on Waverly and Sixth (Sixth Avenue is Avenue of the Americas), two blocks from the northwest corner of the park.
So where does Midge live? The clues are, far enough that he wants a cab, not so far that she even considers there’s a walk other than the park. So I’m thinking southeast corner; I’m guessing around West 3rd and Mercer.