>If you're comparing, say two different types of cars and saying that the comparison is "apples to oranges " then you're mapping meaning.
That's not how linguists define metaphors. Some cursory reading for you:
https://en.wikipedia.org/wiki/Conceptual_metaphor
https://en.wikipedia.org/wiki/Metaphors_We_Live_By
https://www.amazon.com/More-than-Cool-Reason-Metaphor/dp/0226468127
For the record, no you are not mapping meaning between the two cars. You are comparing qualia between the two cars. When you map meaning from one domain to another, you describe both objects by the same terms (the source domain and the target domain). For example, colors (source domain) and emotions (target domain) are both described by colors.
When you compare cars, you don't take terms from one domain, e.g. Honda (source) to describe another domain, e.g. Nissan (target). You describe Hondas by whatever qualia Hondas have (mpg, date of construction, etc.), and you describe Nissans by whatever qualia Nissans have (qualia, date of construction, etc.)