Have in mind a scale drawing (4)
I believe the answer is:
plan
This clue is a double definition.
'have in mind' is the first definition.
(synonyms)
'a scale drawing' is the second definition.
(I've seen this in another clue)
(Other definitions for plan that I've seen before include "Stratagem" , "Method laid out for accomplishing something" , "Large-scale map" , "Scheme, design" , "Devise a way to achieve" .)