Mapmakers in UN censor ad: very unusual (8,6)

I believe the answer is:

ordnance survey

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'mapmakers' is the definition.
I can't tell whether this defines the answer.

'un censor ad very unusual' is the wordplay.
'unusual' indicates an anagram.
'un'+'censor'+'ad'+'very'='uncensoradvery'
'uncensoradvery' anagrammed gives 'ORDNANCE SURVEY'.

'in' acts as a link.

Can you help me to learn more?

(Other definitions for ordnance survey that I've seen before include "Charters" , "UK map makers" , "Geography department" , "UK map-makers" .)

I've seen this clue in The Telegraph.

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