Monday, June 4, 2012

Borders and Territory in Civilization-style Games

This post is the beginning in a series about borders and territory in Civilization-style games.  It is meant to familiarize the reader with the various borders-systems of the Civilization series and sum up how borders are generally integrated into the modern turn-based strategy game.

  • Civilization II (CIV2, 1996)
  • Sid Meier's Alpha Centauri (SMAC, 1999)
  • Civilization III (CIV3, 2001)
  • Civilization IV (CIV4, 2005)
  • Civilization V (CIV5, 2010)

Civilization II

There was no borders system for Civilization II.  The only restriction on city placement were the minimum-distance constraint, and the only way to control AI movement through your land was via Zones of Control from your own units.  Cities could work any tile not being worked by any other city.

Alpha Centauri

Borders were first introduced to turn-based civilization-style games in Sid Meier's Alpha Centauri (SMAC).  Before that time, clear map-level delineations between players did not exist.  In SMAC, borders extended from a faction's bases to a certain, large, radius when the base was first founded.  When borders conflicted, the game used a "who's base is closer" style of adjudication to decide which faction controlled the territory.

Borders could be violated without going to war.  If you discovered another faction's units within your borders, you could demand that they leave, though you faced the risk of them declaring war over the request.  The AI was programmed to not ask for you to leave its borders unless it could see an offending unit.  Importantly, bases could not work tiles not within your borders, and I recall that bases could not be founded in other faction's territory as well.  However, I'm not completely certain about that.

Civilization III

Civilization III introduced the concept of culture related to borders.  Newly founded cities only expanded your borders 1 tile from the city square, and as differing culture levels were reached, the border from the city expanded to the "fat cross" familiar to fans of Civilization 4.  Border conflicts were adjudicated by checking the total value applied to each tile every turn, which each city in range applying its culture value to the tile each turn.  A side effect of this system was that borders were not particularly "sticky" and could change quickly based on founding new cities.

Borders could still be violated without war.  Right of passage agreements would let players use each other's roads and railways, though it also lead to the concept of "RoP Rape" where a player could sign an RoP with an AI, move their units into position around each AI city, and then declare war.  Their units would then be in position to gut the AI empire before any effective response could be mobilized.

The idea of culture-flipping was also introduced.  A city could convert from one civilization to another if it was sufficiently pressured by opposing culture.

Finally, unlike Alpha Centauri, a player could see everything that happened within his borders.

Civilization IV

Civilization IV iterated on the CIV3 design, adding more culture buildings and filling some of the holes.  A player could only enter another player's borders in a state of war or with an open-borders agreement.  Additionally, when war was declared, units were automatically removed to prevent players sneak-attacking the AI.  Tiles and cities also accumulated culture points over the course of the game.  As a consequence, borders became more "sticky" and harder to change as the game progressed.

Culture flips remained, as did the big-fat-cross (BFG).  Below, the city of Aachen has expanded to its 2nd ring borders.  Great Artists were also introduced, and could be consumed to add a large amount of culture in a city to dramatically expand borders.  Early in the game, a properly used GA could overwhelm the established borders of another player.  However, later in the game, due to the accumulation of culture on tiles, the Great Artist bomb became less effective.

2nd ring borders in CIV4

Civilization V

The culture/borders/territory design was mostly rewritten for Civilization 5.  Cities would still gain culture and expand borders based on that culture but tiles would be gained individually.  Tiles could also be gained by using gold to "rush buy" the tile.  However, tiles gained through culture would be gained based on an algorithm outside of the player's control.  My own experience with the tile-picker is that it works reasonably well, but there are certainly instances where I'd prefer a different tile from the one it picked.
City view in Civ5 with predicted tile expansion.  The picker prioritizes luxury resources, but here is torn between choosing the dye or the incense tile.
In CIV5, a player cannot flip tiles from another player without either conquering the offending city or using a Great Artist to culture bomb the tile.  Tiles also did not accumulate culture.  Instead they are assigned to a particular city (either the city whose culture claimed it, or the city working the tile).  Tiles and borders then shift with possession of the city.  This was a dramatic departure from CIV4, where newly conquered territory often needed an influx of culture just to establish a workable border, but was presaged in a CIV III WW2 scenario.  In that scenario, all culture added to a city was given to the current owner.
The same city after the 1st border expansion.


Borders come from culture, generated in cities.  We expect borders to be respected by the AI and other players.  We expect borders to be "sticky": once they're established only dramatic changes can move them.  Effectively, we expect the behavior of borders to mimic those of a real life, sovereign nation state.

Most interesting to me, however, are that borders do not reflect the map terrain. Borders reflect the position of cities and their culture.  Cultural borders do not care whether or not a tile is a plains, mountain, or ocean.  For games which as their basis ask players to plan and grow around the terrain of the map, this seems a strange omission.

In the next post, I'll talk about the differences in game-play between dynamic and static borders.  I plan to take examples from the Civilization series as a whole and a number of Paradox and Creative Assembly titles.