Appalachian English is American English native to the Appalachian mountain region of the Eastern United States. Historically, the term Appalachian dialect refers to a local English variety of southern Appalachia, also known as Smoky Mountain English or Southern Mountain English in American linguistics. This variety is both influential upon and influenced by the Southern U.S. regional dialect, which has become predominant in central and southern Appalachia today, while a Western Pennsylvania regional dialect has become predominant in northern Appalachia, according to the 2006 Atlas of North American English (ANAE). The ANAE identifies the "Inland South", a dialect sub-region in which the Southern U.S. dialect's defining vowel shift is the most developed, as centering squarely in southern Appalachia: namely, the cities of Knoxville and Chattanooga, Tennessee; Birmingham, Alabama; Greenville, South Carolina; and Asheville, North Carolina. All Appalachian English is rhotic and characterized by distinct phonology, morphology, syntax, and lexicon. It is mostly oral but its features are also sometimes represented in literary works.