What about smaller scale diaspora identities? My wife is a Pittsburgh native and when she meets another member of the Nation, the conversation almost always turns to the part of the Burgh where she grew up and what high school she attended. She's from the North Hills and if the fellow Diasporan is also from that area, the game is on, "We went to the same elementary school!"
To emphasize my point, I offer another tale of Florida-based Pittsburgh connectivity, but at the smaller scale of McKeesport:
They talk about roller skating at Olympia Park, about eating Klondike bars, about the sawdust floors at Balsamo's grocery store, about the smells of Stalling Bakery, about dancing at the Palisades and shopping at G.C. Murphy Co.
They drink coffee and eat dessert and laugh about old times.
They talk about how strange it is that they all walked the same hallways 1, 000 miles away, and how they ended up here, standing shoulder-to-shoulder in the same living room for a photograph.
Eating Klondike bars isn't specific to McKeesport, but the other common experiences reveal a tighter geography of trust. I think the Balkanized political landscape of Pittsburgh is something that the Burgh Diaspora all share. There is a collective Pittsburgh pride that covers the region, but the shared sense of home is something (somewhere) much more esoteric.
Just how unique is Pittsburgh's parochial mindset?