truthsharer: R’ Moshe held that there’s a big difference between Brooklyn and Queens. Halachically, he said Brooklyn is considered as one city, while Queens is considered as multiple small ones. The reason was that if you mail a letter to someone in Brooklyn, you write “Brooklyn, NY”. You don’t write Flatbush or Boro Park, you write Brooklyn.
If you mail a letter to Queens, you don’t write “Queens, NY”. You write Kew Garden Hills, or Flushing, etc.
That also explains why each community in Queens has its own eruv, and some people hold you shouldn’t carry from one to the other on Shabbos.