When Ralph marks his route to New York City on the map, he starts at a point in the center of Pennsylvania. There is no real town of Chatsburg in PA, but there is a town near his starting point called "Bellefonte" (the character Ralph Burton in the movie is played by Harry Belafonte).
To film the striking images of a deserted New York City, the cast and crew had to start filming at dawn in order to capture the city before the early morning rush. This gave them no more than an hour or two per day in which to film the sequence.
On the bookshelf behind the bed in which Ben Thacker is recovering, is a copy of "The Proud Land" by James Lee Bartlow. This is the book supposedly written by Bartlow, played by Dick Powell in The Bad and the Beautiful (1952).
The three survivors watch two "News of the Day" news reels. The first is "Faulty Wire Trips the Vanguard" (1958) with commentary by Michael Fitzmaurice, although only 25 seconds (from 0:30 to 0:55) of the 63-second news reel is shown in the movie. The second is "World Lovelies Take Ferris Ride" (1959) with commentary by Peter Roberts showing candidates for the Miss Universe contest at Palisades Park, New Jersey. The copyright date of the second news reel is unreadable and appears to have been made out of focus on purpose.
The montage of the lion statues when Ralph rings the bell at St. Patrick's Cathedral is an homage to the stone lion montage in Battleship Potemkin (1925) and is also parodied in Woody Allen's Sleeper (1973).