Check out these links to read more about the real places:
Great Buildings Online entry for Flatiron Building
"The Flatiron Building at 100" on Flatironmag.com
Library of Congress film of a windy day at the Flatiron Building and the possible origin of the phrase "23 Skidoo"
The official site of the Empire State Building
Emporis entry for Empire State Building
Great Buildings Online entry for Empire State Building
Lewis Hine photographs of the building construction: at Columbia and NY Public Library
NPR program about the history of the tower