Border expansion

General Principles

Unlike the Civilization series of games, border expansion is entirely deterministic. It is also not dependent on culture.

Your borders will expand to “join up” if you control the tiles all around it, so you won’t be left with tiny “holes” in your borders around your Kingdom.

When your borders expand, the default is 1 tile adjacent but if the next tile beyond that is a special or an urban tile, then your borders will expand to encompass the special/urban tile as well, so the “right” border expansion can net you an impressive number of tiles indeed, and is almost a mini-game of its own.

How to Expand Your Borders: Increasing the Number of Workable Tiles

Ultimately, the number of workable tiles a city has at its disposal is a function of its borders. As a city’s borders cast an increasingly wider net, you get more tiles to play with, and there are several things you can do to help speed that along. Here are the major ones:

• Urban tile improvements built on your border (examples include Shrine, Monastery, Hamlet) will extend your city’s borders.
  • Builder leaders can build empty urban tiles.
• Train Specialists – Training specialists may expand your borders, provided that the tiles adjacent to the tile the specialist was trained on are not currently inside your borders.
• Events – Sometimes, you’ll get an event which has an option to expand a city’s border tiles.
• Colonies – This law allows you to buy tiles not yet enclosed by any city’s borders. The tile acquisition cost starts out very low but can scale rather quickly.
• Landowners Family – Founding the “Seat” of the Landowners family allows you to buy tiles for that city from the turn of founding.
• The Border Boost Bonus Card – Available at Aristocracy, this card will grant a few extra tiles to every city you have when you complete the research on the card.

City Founding Rules

When you found a city, you always get:

• All tiles in a one tile radius from all the site's urban tiles
• All tiles in a 2 tiles radius from the city center (the exact spot you settle the city)

Then you have all the criteria for additional expansion as below

Border Expansion Rules

• Borders spread to resources when owning an adjacent tile without a resource on it

• Borders spread to urban tiles when owning an adjacent tile

• Urban tiles spread borders to all adjacent tiles

• Specialists spread borders to all adjacent tiles

• Borders spread to resources when owning an adjacent tile without a resource on it

• Borders spread to mountain tiles when you own two adjacent passable land tiles

• Borders spread to water tiles when owning two adjacent land tiles or one adjacent passable land tile if there are no other passable land tiles adjacent to both the water and owned land tile

• Borders spread/collapse onto tiles with owned tiles on directly opposite sides.

Any border spread from the above rules can itself cause extra spread following these rules i.e. spreading to a resource tile can then add adjacent water tiles, which can then collapse borders if it leaves a hole.

Examples

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  Example of border expansion. Building a specialist at the Nets gives all the yellow tiles. Because the western yellow tile borders an urban tile, all tiles surrounding the urban tile are granted -- the red tiles. And because the east most blue tile is a water tile that has at least 2 land tiles bordering it, it's granted -- which in turn grabs the resource tile adjacent.