DO CAMERAS MAKE CITIES SAFER? Some leaders are calling for more surveillance cameras, particularly in transportation systems and other spots vulnerable to terrorism.

WHERE CAMERAS ARE USED ALREADY: Some 5,000 surveillance cameras are already in use in New York across all modes of city travel; Chicago has at least 2,000 cameras.

STILL NOT A PERFECT SOLUTION: Experts say that despite London’s huge network of cameras, the bombings weren’t prevented. Others believe the cameras at best only encourage terrorists to shift their target.

By The Associated Press