NYPD's ComStat system, a computerised map of criminality in the city, has made a huge difference.

ECONOMIST: New York��s police

Comstat, for example, was devised by the Big Apple's former police chief, William Bratton, and his colleague, Jack Maple (who has been an adviser to New Orleans).

ECONOMIST: Crime and cities

If I were president of the United States, I could do something about that by deploying a fence, by deploying a virtual fence, by having a BorderStat system like my COMSTAT system that brought down crime in New York, and just stopping people from coming in, and then having a tamper-proof ID card.

CNN: Giuliani's responses at the CNN/YouTube debate