Complex sentence: There are over 1,000 pizzerias and "slice shops" in NYC, and many purvey both whole pies and slices, but the majority of overall sales among NYC pizzerias is based upon slices.
Split into simpler sentences: There are over 1,000 pizzerias and "slice shops" in NYC, and many purvey both whole pies and slices. The majority of overall sales among NYC pizzerias is based upon slices.