A line on a map which represents the geographical boundary of regional linguistic variants. By extension, the term also refers to the dialect features themselves. For example, in the USA north of the Mason–Dixon line, the word greasy is pronounce with an ‘s’; south of the line, it is sounded with a ‘z’ (L. Campbell 2004). Isoglosses are usually highly simplified representations and do not depict an abrupt transition. Sometimes, a bundle of isoglosses may occur, where a number of isoglosses lie close enough together to indicate a true dialect boundary; see W. Wolfram and N. Schilling-Estes (1998).