Superman was filmed almost 40 years ago (can you believe it?) so it is not very surprising that the directors would make use of clever props and models. Yes, this classic movie was also not filmed on a life size movie set, but was cleverly filmed with the use of a miniature movie set (just take a look at how the actors literally dwarf the props)!
When Christopher Reeve was seen impressively flying, this was not due to his magic ability but actually the work of early green screening with him lying on a board. Highly innovative for its time!