With a gunman raining bullets down on a crowd of Las Vegas concertgoers in October, police officers who rushed into the hotel where he was holed up struggled at first to figure out what floor he was on.

That quandary — and the many other difficulties of disarming a high-rise sniper — have informed how the New York Police Department is preparing for hundreds of thousands of people to gather in Times Square on New Year’s Eve.

The event has long drawn a heavy security presence. But this year the police said they would send rooftop observation teams and counter-snipers into more buildings. Officers will be patrolling hotels in the days leading up to the ball drop on New Year’s Eve.

And for the first time, the Police Department is planning to attach reflective markers to the outside of buildings at certain intervals so that in the event of an attack, officers can quickly figure out what floor a gunman is on.