Church painting is map (5)
I believe the answer is:
chart
'is map' is the definition.
(I've seen this in another clue)
'church painting' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'painting' becomes 'art' (painting is an art).
'ch'+'art'='CHART'
(Other definitions for chart that I've seen before include "Table or diagram" , "what could be a pie" , "Plan" , "Hit parade" , "Marine map" .)