Map makers or graph creators, possibly (13)
I believe the answer is:
'map makers' is the definition.
('cartographer' can be a synonym of 'map maker')
'graph creators possibly' is the wordplay.
'possibly' is an anagram indicator.
'graphcreators' is an anagram of 'CARTOGRAPHERS'.
'or' acts as a link.
(Another definition for cartographers that I've seen is " Map makers".)