Possible Clues:

• One thus joins the jolly line
• Theory incorporating different line that's charted to a degree
• Wavy line on some maps
• A line on a map joining places of equal temperature
• Head of Meteorology differs, first drawing line on her map
• Line on map is not the same motorway
• Feature of meteorological chart in middle of this other map
• What's on meteorologist's chart as part of his other map
• Line on a map linking places of equal temperature
• Distinctive theory about extra meteorological line