Church painting is a map (5)
I believe the answer is:
chart
'map' is the definition.
(I know this)
'church painting' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'painting' becomes 'art' (painting is an art).
'ch'+'art'='CHART'
'is a' is the link.
(Other definitions for chart that I've seen before include "series of plots?" , "Table or graph" , "Visual display of information" , "Table or diagram" , "Hit parade" .)