Found primarily in operational games and higher level tactical games, a unit's zone of control is usually said to be the 6 hexes immediately surrounding said unit. Every game handles ZOC differently. Sometime different terrain features negate ZOC, and often a friendly unit will negate is as well.
This is the ZOC rule from No Retreat: The Russian Front from GMT
Zone of Control. The area of effect surrounding a unit; usually defined as the six immediately adjacent hexes. In theory, the exact character of a Zone of Control in a given game-system may be delineated by the use of a combination of adjectives, taking one from each of the following groups:
Effect on Movement:
Locking: Units must stop upon entering an Enemy controlled hex and may leave only as a result of combat.
Rigid. Units must stop upon entering an Enemy controlled hex and may leave only at the beginning of a Movement Phase.
Elastic. Units may enter and leave Enemy Zones of Control by paying an additional cost in Movement Points.
Open. Zones of Control have no effect on Movement.
Effects on Combat:
Active. Requires that every Enemy unit in a Friendly Zone of Control be attacked in the Combat Phase.
Inactive. Makes no requirement for attack.
Effect on Supply Line and Retreat:
Interdicting. Prohibits the path of retreat or supply form being traced through an Enemy controlled hex regardless of the presence of Friendly units.
Suppressive. Prohibits the path of supply or retreat from being traced through an Enemy controlled hex if the hex is not occupied by Friendly units.
Permissive. Does not affect the path of supply or retreat in any way.
Example. A Ridge, Active, Suppressive Zone of Control.
Note that if units have an Open, Inactive, Permissive Zone of control they in fact have no Zone of Control.
