One of the primary purposes of any one nation's military is in the defense of one's own borders - shared borders complicate such defending.
Border Coverage is the complete distance of shared borders for a given nation. Borders become important in forging alliances and managing incoming/outgoing road/foot traffic. In times of war, borders become increasingly important for the home guard to defend. For the purposes of the GFP ranking, lengthy shared borders requires a greater material and financial commitment to national security.
Values below displayed in Kilometers (km). Island-nations, such as Australia, are not penalized for lacking shared borders.