It's used in the field of statistics in place of saying "for each person". Bad phrasing (I seem to get accused of that alot lately). I was kind of going for 'There is more rain on the people of New York than of Seattle.'
Wikipedia:
"At 944 mm (37.49 in.), in reality, the city receives less precipitation annually than New York City (1201 mm/47.28 in.), Atlanta (1290 mm/50.79 in.), Boston (1055 mm/41.53 in.), Baltimore (1038 mm/40.87 in.), Portland, Maine (1128 mm/44.41 in.), Jacksonville, Florida (1304 mm/51.34 in.), and most cities on the Eastern Seaboard of the U.S. However, Seattle's rain is rather constant and misty, versus New York City's rain, which is infrequent and heavy."