Brooklyn as a Single City
Brooklyn neighborhoods are connected by one street grid, major avenues, transit, bridges, tunnels, and continuous public movement.
One continuous urban network
Brooklyn's neighborhoods are joined by avenues, local streets, buses, rail lines, commercial corridors, and continuous development. People pass between them without crossing a city wall or controlled gate.
Bridges and tunnels then connect the borough to Manhattan, Queens, Staten Island, and the wider region. A route inside one neighborhood remains part of that larger public system.
Neighborhood names do not create walls
Cultural boundaries, ZIP codes, community-board lines, and familiar neighborhood names help describe Brooklyn. They do not close streets or reduce the public using them.
A proposed eruv may draw its own perimeter, but that perimeter must be halachically valid and must address every road passing through it. The name Crown Heights cannot perform that work.
Rav Moshe's approach to Brooklyn
Rav Moshe's responsa repeatedly resist treating a small neighborhood as though it were disconnected from the city around it. His analysis looks to the population and public roads of the larger urban reality.
This approach appears in his discussions of Flatbush and Boro Park and in his refusal to establish the proposed Brooklyn eruv. It forms the major large-city background to the Crown Heights question.