Crossword Genius

Boris a problem making line on map? (6)

Ross

I believe the answer is:

isobar

'line on map?' is the definition.
(line indicating pressure on a map)

'boris a problem' is the wordplay.
'problem' indicates anagramming the letters.
'boris'+'a'='borisa'
'borisa' anagrammed gives 'ISOBAR'.

'making' acts as a link.

(Other definitions for isobar that I've seen before include "Map line showing atmosphere pressure" , "Line on map showing barometric pressure" , "Line showing points having equal barometric pressure at a given time" , "A Boris (anag.)" , "meteorologist's line" .)

I've seen this clue in the Sydney Morning Herald.
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