Indian city in dark plan (7)
I believe the answer is:
diagram
'plan' is the definition.
(I've seen this before)
'indian city in dark' is the wordplay.
'indian city' becomes 'agra' (I've seen this before).
'in' is an insertion indicator.
'dark' becomes 'dim' (similar in meaning).
'agra' going into 'dim' is 'DIAGRAM'.
(Other definitions for diagram that I've seen before include "Explanatory figure" , "Outline drawing showing parts or workings" , "scheme" , "Drawing to show how things work" , "A grid, Ma? (Anag)" .)