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