Possible Clues:

• Line in front causes obstruction: none must enter
• A biro's possibly used to make line on map
• Line connecting points of the same atmospheric pressure
• Boris frantically pens article, it indicates pressure?
• One shows atmosphere exists over the legal profession
• Line on a map linking places of the same atmospheric pressure
• Line on map observed at first in island pub
• Certain line on a weather map
• Line on certain maps represents old pub
• Line connecting places of equal pressure