The way I understand ethnic enclaves, they spring up randomly usually in poorer areas where new immigrants can afford to settle. After those folks get established, the next wave/waves come and join them in the same neighborhoods to help their adjustment, get them set, help them find work, support system etc. After this, places with the history and that still have a strong connection to that history will have their neighborhood renamed and recognized by the city. Historic Filipinotown in LA got the name back in the early 2000s i think, and its like 4 square blocks