Set off from location south of service area (12)
I believe the answer is:
counterpoint
'set off' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'location south of service area' is the wordplay.
I cannot quite see how this works, but
'location' could be 'point' (point is a kind of location) and 'point' is located in the answer.
'of' could be 'o' and 'o' is found within the answer.
This explanation may well be incorrect...
'from' is the link.
Can you help me to learn more?
(Other definitions for counterpoint that I've seen before include "Foil" , "Combination of melodies" , "Melody added to another" , "Interplay of melodies" , "Compensate for" .)