New York City has long been called by many “the greatest city in the world.”
 
The television show “The Late Show with David Letterman” broadcasts from the Ed Sullivan Theater, at Broadway between West 53rd and West 54th Streets (“Big Apple Corner”). A show on September 17, 2001 discussed the recent attack on the World Trade Center. Ever since then, the opening tagline has been “From New York, the greatest city in the world.”
 
   
Internet Movie Database
“Late Show with David Letterman” (1993) [TV-Series 1993-????]
Tagline: From New York, the Greatest City in the World.
Plot Outline: The Late Show with David Letterman is an hour-long weeknight comedy and talk-show broadcast by CBS from the Ed Sullivan Theater on Broadway in New York City.
   
Wikipedia: David Letterman
Before September 11, various descriptions were affixed to New York City at the beginning of the show, but starting with the 9/17/01 show and continuing indefinitely, announcer Alan Kalter introduces the show “From New York, The Greatest City in the World, it’s The Late Show with David Letterman!”
 
Wikipedia: Late Show
On September 17, 2001, The Late Show returned to the television airwaves six days after the September 11th attacks, a high-profile appearance given the anxiety and grief still felt by many at the time, especially in New York City. Letterman reportedly was considering not resuming the show, and credited “the reason that I am doing a show and the reason I am back to work is because of Mayor Giuliani…. Rudolph Giuliani is the personification of courage.”

In his opening monologue, an emotional David Letterman said:

“The reason we were attacked, the reason these people are dead, these people are missing and dead ... They weren’t doing anything wrong, they were living their lives, they were going to work, they were traveling, they were doing what they normally do. Uh, as I understand it—and my understanding of this is vague, at best—another smaller group of people stole some airplanes and crashed them into buildings. And we’re told that they were zealots fueled by religious fervor, religious fervor. And if you live to be a thousand years old, will that make any sense to you? Will that make any goddamned sense?”
 
That night Letterman hosted Dan Rather and Regis Philbin. The Dan Rather interview was one of the most emotional interviews in the history of the show, with both David and Dan Rather holding back tears while speaking about the attacks.

Since then, the regular opening, which had previously made fun of New York City, has consistently led with “From New York… the greatest city in the world…” These words have been omitted from the opening of each episode with a guest host, however.