Distance has an important impact on many aspects of game-play.
Diplomatic actions are restricted by distance, and is also an important modifier in several diplomatic actions. In war, it is important as it impacts the speed of armies and fleets, and it impacts many other aspects of game-play as well.
The distance between two land provinces can be viewed in tooltips, by clicking on province and then hovering another.
Diplomacy
Diplomatic actions are limited by distance. Most require being within diplomatic range: 700 distance from their nearest controlled province. Having the same religion, culture group and culture as the target of your action extends the diplomatic range by 100 each.
Some diplomatic actions have stricter requirements:
- Joining a defensive pact is limited by distance: a distance within 300 is required for same religion group and a distance within 400 is required for a different religion group.
Seduction is limited by diplomatic range and also slows down with distance (starting at 200 distance)
AI behavior is also affected by distance:
- AI vassals are more likely to join an independence faction if they are far from their liege's capital
- AI rulers may join in defense against holy wars if the capital-to-capital distance is 200 or less (or if the realms are neighbors)
Warfare
Province distance affects the time it takes armies and fleets to move between provinces (see Warfare#Movement_speed).
Mercenaries
The mercenaries a ruler can hire is determined by the distance between the ruler's capital and the mercenary's capital.
Trade posts
The price of a merchant republic trade post is increased by 30% times the distance from the closest controlled holding. See Trade_post#Merchant_republic_trade_posts for details.
Adventurers
The titles that adventurers target are also dependent on distance. The casus belli that non-claimant adventurers use is required to target a title within a distance of 800.