A cline could also include items that go from weak to strong, or frequent to rare for example.
Example
The teacher asks learners to map modal verbs of probability such as ‘must', ‘might not' and ‘may' on a cline of probability from 100% sure to 100% not sure.
In the classroom
Clines can be a useful tool for learners to record information, and they can help teachers as a concept check. However, a learner's ability to use a cline does not mean that they can use the target language in context.
Further links:
https://www.teachingenglish.org.uk/article/conveying-meaning
https://www.teachingenglish.org.uk/article/checking-understanding