An isogloss tells us only that there has occured somewhere and at some time a sound- change, an analogic-semantic change, or a cultural loan, but the isogloss does not tell us where or when this change occurred.
- Bloomfield (1935), a pag.480

Within a dialect area, we can draw lines between places which differ as to any feature of language. Such lines are called 'isoglosses'.
- Bloomfield (1935), a pag.51