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NEW YORK (AP) The New York Police Department says a large balloon is being unleashed above the city for two days to measure the heights of the city's buildings.

The police department said the balloon will remain aloft for about nine hours on Sunday in lower Manhattan and more than 13 hours on Monday in midtown.

Police said the balloon will be about 800 feet in the air as it collects data for a private architecture firm conducting height surveys of Manhattan buildings.