Crossword Genius

Line on map, one originally standing on counter (6)

Ross

I believe the answer is:

isobar

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

'one originally standing on counter' is the wordplay.
'one' becomes 'I' (Roman numeral).
'originally' indicates taking the first letters.
'counter' becomes 'bar' (bar is a kind of counter).
The first letters of 'standing on' is 'so'.
'i'+'so'+'bar'='ISOBAR'

(Other definitions for isobar that I've seen before include "meteorologist's line" , "Meteorological line joining points of equal pressure" , "Line showing points having equal barometric pressure at a given time" , "What's shown on some maps" , "Line of equal barometric pressure on a map" .)

I've seen this clue in The Times.
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