One of the most important explanations for the emergence of dialects in America starts with the settlement patterns of the original groups of speakers. These first settlers typically establish a cultural and linguistic area that persists through time, even though certain aspects of their speech will inevitably change. Adjacent land is occupied and settled and the identity of the new culture emerges, as a cohesive society develops in the region. These cultural encounters will affect the expansion and development of the dialect. Once settlement locations are established, dialect boundaries will often follow the major migratory routes from these initial points.
Migration patterns vary over time and are unique to different cultural groups.
They can involve geographical movement as well as movements from rural to urban settings. When we cite the significance of physical boundaries, we are really talking about lines of communication, and the fact that discontinuities in communication have taken place between communities due to physical conditions. Think about how the suburbs are designed as a sort of self-imposed isolation. Along the paths of resettlement and migration, contact with other language groups often takes place. This contact can influence both general language and specific dialect formation as the languages borrow from each other.