
1) Line on a map of dialects
Found on
https://www.crosswordclues.com/clue/isograph

Image taken from People Play UK, a UK government funded project to make the theatre collection of the V&A available to the public. http://www.peopleplayuk.org.uk/collections/object.php?object_id=1472 PeoplePlayUK allows reproduction and reuse of items accessed through the website for non-commercial educational and research purposes (as required by...
Found on
http://en.wikipedia.org/wiki/Isograph

line connecting points of same linguistic usage in some respect
Found on
http://phrontistery.info/i.html

(in the study of the geographical distribution of a dialect) a line drawn on a map to indicate areas having common linguistic characteristics.
Found on
https://www.infoplease.com/dictionary/isograph
No exact match found.