Zones of Control, abbreviated as ZOC, is a game concept which prevents you moving freely in zones controlled (or partially controlled) by enemy forces.
The general rule is that a land unit which is adjacent to an enemy occupied square cannot move directly to another square which is also adjacent to an enemy occupied square. Here an enemy occupied square means a land square with an enemy unit on it. Adjacency means any of the eight squares surrounding a unit.
In the following special cases ZOC does not apply:
- A unit moving directly into or out of a city.
- A unit moving onto a square occupied by a friendly unit.
- A unit moving from an ocean square (disembarking from a boat).
- A unit type which explicitly ignores ZOC, eg Diplomats and Spies.
- Only land units are restricted by ZOC.
- Non-land units can impose ZOC (that is, count as enemy occupied squares), but only if they are on a land square. So effectively sea units cannot impose ZOC (unless they are in a city), and air units (including helicopters) do not impose ZOC if they are over ocean squares.
- ZOC does not restrict unit attacks, only movement.
- An enemy city counts as an enemy occupied square if there are any units inside the city, but not if the city is empty. This is the same rule as for any other square).
- Moving from an ocean square is a special case; moving _to_ an ocean square (moving back onto a boat) is also permitted, by the special case of moving onto a friendly unit (the boat).
You can infiltrate enemy zones by first moving in a Diplomat (or some other unit which ignores ZOC), and then moving regular units onto the square now occupied by the Diplomat. By repeating this process (and optionally leaving some units behind to keep squares occupied), you can make a path through enemy territory.
These rules differ slightly from previous versions of Freeciv (release 1.8.0 and before) in the following ways:
- Enemy cities with no units in them no longer impose ZOC.
- The special case for land units disembarking is new.