Crossword Genius

Map-maker and former president in possession of round plot (12)

Ross

I believe the answer is:

cartographer

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'map-maker' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for cartographer that I've seen before include "Map-maker" , "Map maker" , "One making maps" , "one making plans" .)

I've seen this clue in The Times.
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