By Mail Game
Advantage, as its name implies, is determining which of two units gets the drop on another. Most times this is determined how long a unit is in a territory.
Any unit that is camped in or patrolling a territory first gains the advantage on any entering units. The camped units can make a cursory estimation of the size of the incoming units and their type. In addition, the camped unit may choose to hide and stay out of the way of the incoming unit. The only exception to this rule is that any unit without the ability to gain advantage naturally (such as a scout) has no advantage in territories that have a settlement.
Ties in Advantage
When there is a tie of advantage both parties are alerted to the others presence.
Units With Advantage
Scouts are the earliest units that have advantage. They gain advantage if they enter the same area as a unit that does not naturally gain advantage. Any scout that has camped in an area or is patrolling an area gains advantage over a scout entering that same area.
Town Guard and its analogous parts also gain advantage on any unit moving directly into its city.