Related Clues:

• One's additional mark a feature of weather map
• Mother is over the line
• I 'cry a river' -- it shows you the pressure!
• Line on map is round and local
• First from optic in one's pub -- an indication of pressure?
• Pressure line
• Curve of equal temperatures
• A Boris (anag.)
• It's displayed by weatherman in his other map
• Temperature line more confused with this
• Weather line on map -- one thus gets temperature on island
• I accordingly must join legal group on which pressure is constant
• Line on a map linking places of equal temperature
• I'm high-flying Brit in meteorological line
• What's on meteorologist's chart as part of his other map