Why they exist. A community district is a unit of local review and service delivery. A 1,100-acre park or an international airport does not sit inside a neighbourhood, so the City maps it separately instead of splitting it between the boards around it.
What it changes in practice. Look up an address inside one and the card shows zoning, land use and every other district line, but no community board. That is correct, not an error. Review responsibility is shared among the boards that border it.
The clearest live example. Citi Field and the USTA Billie Jean King National Tennis Center both sit in Queens JIA 81, Flushing Meadows Corona Park, bordered by six Queens boards. When Mets ownership proposed the Metropolitan Park casino complex on the Citi Field parking lot, the land was legally mapped parkland even though it is asphalt, so it needed zoning text and city map amendments rather than an ordinary rezoning, and several adjacent boards each took it up.
Two of them cross borough lines. Floyd Bennett Field and Gateway (Brooklyn JIA 56) borders Queens CB 10, and Forest Park (Queens JIA 82) borders Brooklyn CB 5. So a Queens board and a Brooklyn board can share an interest in the same ground.
Randall’s Island is not one. It reads like it should be, but it is part of Manhattan CB 11.
How this page was built. Every area was identified by testing a known landmark inside it against the City’s own community district boundary file, NYC Open Data 5crt-au7u. The bordering boards were computed from those same polygons, not taken from a list. Every example address was checked against the live address card.