Is wild boar shown on a chart? (6)

I believe the answer is:

isobar

I'm a little stuck... Click here to teach me more about this clue!

'shown on a chart?' is the definition.
I can't tell whether this definition defines the answer.

'is wild boar' is the wordplay.
'wild' indicates an anagram.
'boar' with letters rearranged gives 'obar'.
'is'+'obar'='ISOBAR'

Can you help me to learn more?

(Other definitions for isobar that I've seen before include "Line on a map connecting points of equal atmospheric pressure" , "Line in front" , "curve on map" , "Line on map indicating atmospheric pressure" , "Line on map showing barometric pressure" .)

I've seen this clue in the Evening Standard.

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