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".
Maps can depict clines visually using lines that show how character traits change across a geographical area.  These lines are called clines and represent the transition between different character states.  Ernst Mayr defines isophenes, which are lines representing equal expression of a trait that varies clinally.