The most common and most likely answer to this crossword clue is the 8 plus 6 letter word ORDNANCE SURVEY
I've seen this crossword clue in Financial Times
O
R
D
N
A
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C
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S
U
R
V
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More clues leading to the result ORDNANCE SURVEY
Buddy explains!

The straight part
We know that "Those making maps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case those making maps = ordnance survey.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.