Clines can be portrayed graphically on maps using lines that show the transition in character state from one end of the geographic range to the other. Character states can however additionally be represented using isophenes, defined by Ernst Mayr as "lines of equal expression of a clinally varying character".
The passage describes how clines, lines representing transitions in character states, are depicted on maps. It also introduces isophenes, defined by Ernst Mayr as lines of equal expression for clinally varying characters.