When two or more Jews get together and discuss who knows who's Jewish friends and relatives from where.
Shem tov: You know my brother Morty from New York, he's a doctor, married to Rachael?
Herschel: Yes, I once went out for bagels with him at my cousin Eli's diner in Long Island. Oy, you should have seen the savings!
Passerby: What a Jewish Geography!