New York has long been a city of immigrants, but linguists now consider it a laboratory for studying and preserving languages in rapid decline elsewhere in the world.
This is an excellent video for showing the diffusion of languages in the era of migration to major urban centers. It also shows the factors that lead to the decline of indigenous languages that are on the fringe of the global economy and the importance of language to cultural traditions. Here is the article related to the video available.
Via Seth Dixon