This source gives us a background on Vietnamese immigration to the US. It includes maps on how and where the Vietnamese populations are concentrated.
Chuong, Chung Hoan and Minh Hoa Ta. 2003. “Vietnamese Americans” Asian-Nation: The Landscape of Asian America. <http://www.asian-nation.org/vietnamese.shtml> (September 20, 2013).
The authors are Vietnamese themselves. The background and estimated amount of immigrants coming from Vietnam are discussed. The cause and effect is mentioned. There is also a part of the effect of the immigration wave on US economy and culture.
Povell, Marc. 2005. ” The American Immigration Law Foundation: The History of Vietnamese Immigration”. (September 20, 2013).
More background about the Vietnamese immigrant waves. The author is not Vietnamese. He discusses the first wave, war refugees. The second wave was filled with disgruntled post-war immigrants. There is also information about how spread out Vietnamese communities are, and the geographical locations that they prefer.