New York, Los Angeles, and Miami are primate immigrant centers within the U.S. metropolitan system, attracting new immigrant arrivals as well as serving as focal points for internal migrants. Using the segmented assimilation framework as a foundation, this paper emphasizes the role of geography and migration within the assimilation process. Focusing upon selected origin groups, migrant selectivity and the determinants of migration are evaluated and compared, highlighting the differential role of primate centers. While the New York and Miami metropolitan centers clearly dominate Dominican and Cuban migration systems respectively, the role of primate centers is less clear among other national origin groups. [ABSTRACT FROM AUTHOR]