Understanding the Zone Of Control
limiting the enemy movements

Introduction

The zone of control (ZOC) is an important aspect of unit movement during combat. The ZOC rule limits the movement of units that are adjacent to enemy units and can be used to protect ranged units, for instance. But misunderstanding this rule may be fatal during a campaign, especially when facing a mobile enemy. This article explains why.


Key concepts / Abbreviations
Definition of the Zone Of Control
Applying the rule
Special cases
Dealing with the Zone Of Control
Known Issues
Conclusion

Key Concepts / Abbreviations


Combat Unit – a military unit that can engage in combat against other units or against cities.
Non-Combat Unit (aka Civilian Unit) - a unit that cannot fight, i.e. Settlers, Workers, Work Boats, and Great People (of particular importance, the Great General)
Embarked Unit - a land or civilian unit that is on a water tile.
MP - movement point
LOS - line of sight
ZOC - zone of control


Definition of the Zone Of Control

"Combat units exert a “Zone of Control” (ZOC) over the tiles around them. When a unit moves between two tiles within an enemy’s ZOC it expends all of its MPs."
(Civilization V manual, page 53)


http://forums.civfanatics.com/attachment.php?attachmentid=305907&stc=1&d=1320359371
Understanding the ZOC rule with some caravels.
This rule must be interpreted as follows:

ZOC: zone of 6 hexes adjacent to a combat unit

ZOC rule: if a unit directly moves one tile within the same enemy's ZOC, it expends all of its MPs.


Let's take the French Caravel as shown on the right.
As with every combat unit, it has its own ZOC (delineated in red).
The rule applies to enemies present in the ZOC, like the Roman Caravel, but not necessarily to all enemy movements:


Only direct moves within the (same) ZOC are affected (red arrows)

Other moves are NOT affected. In particular the rule does NOT apply:

if an enemy enters or exits the ZOC (blue arrow)
if an enemy exits the ZOC and at the same time enters another ZOC (green arrow)
if an enemy exits the ZOC and reenters it later (yellow arrow)




Applying the rule


The following examples illustrate typical cases of the ZOC rule.
(Civ V release 1.0.1.383 was used for testing)

Blocking enemy units

Fig. 1: the Longswordsman cannot attack the Crossbowman due to the ZOC of the Pikeman.http://forums.civfanatics.com/attachment.php?attachmentid=307625&stc=1&d=1321987210
Fig. 1b: the French Trireme can only move 2 tiles to the east due to the enemy's ZOChttp://forums.civfanatics.com/attachment.php?attachmentid=307627&stc=1&d=1321987559

Entering and/or Exiting a ZOC does not impede unit's movement

Fig. 2: the French Infantery may enter the enemy ZOC and then exit it and continue its movement, as if there were no ZOC.http://forums.civfanatics.com/attachment.php?attachmentid=307831&stc=1&d=1322222536

Walking through the enemies

Fig. 3: the Horseman can withdraw because he first exits the Pikeman's ZOC and enters the Archer's ZOC, and then continues his movement one tile within the Archer's ZOC. http://forums.civfanatics.com/attachment.php?attachmentid=307633&d=1321988677

Exiting and reentering the ZOC with mobile units (3-4 MPs) to flank the enemy!

Fig. 4: the Horseman exits the enemy ZOC, reenters it and may attack the Archer in the same turn!http://forums.civfanatics.com/attachment.php?attachmentid=307632&d=1321988554

Fig. 4b: the Trireme can escape because it exits the enemy ZOC, reenters it and may continue its movement.http://forums.civfanatics.com/attachment.php?attachmentid=307631&stc=1&d=1321988311

Zigzagging around the ZOC with fast units! (> 4 MPs)

Fig. 5: the Battlehip is not really blocked by the enemy, just slowed down.http://forums.civfanatics.com/attachment.php?attachmentid=330392&stc=1&d=1346586654



http://forums.civfanatics.com/attachment.php?attachmentid=307624&stc=1&d=1321986727
The Trireme can make a sally because embarked units have no ZOC !Special cases


Cities

Cities exert a ZOC too, even if there is no garrison. A city ZOC applies to naval and to land units. (see Fig. 6)
Combat units also exert a ZOC on enemy units stationed in a city. (see Fig. 7)



Embarked Units

Embarked combat units do NOT exert a ZOC. (see Fig. 8)
Land and naval units exert a ZOC on embarked units. (see Fig. 11)



Naval Units vs Land Units

Naval units exert a ZOC on enemy naval units. (see Fig. 1b)
Naval units also exert a ZOC on enemy land units. (see Fig. 9)
Land units do NOT exert a ZOC on enemy naval units. (see Fig. 10)



Units able to move after attacking

A unit that can move after attacking (e.g. a mounted or an armored unit), can kill an enemy within another enemy's ZOC and still continue moving. (see Fig. 11b)



Miscellaneous

Only combat units exert a ZOC: non-combat units do NOT. But non-combat units must respect the ZOC of enemy units.

The ZOC rule does not apply at all to air units






Examples and figures


Fig. 6: the Rifleman cannot kill the General due to the city's ZOC.
http://forums.civfanatics.com/attachment.php?attachmentid=307636&d=1321989987
Fig. 7: the Warrior exiting the city is concerned by the Barbarian's ZOC.
http://forums.civfanatics.com/attachment.php?attachmentid=307637&d=1321989987
Fig. 8: the Trireme is not blocked by the embarked enemy.
http://forums.civfanatics.com/attachment.php?attachmentid=307638&d=1321989987
Fig. 9: the Warrior's movement is limited by the Barbarian Galley.
http://forums.civfanatics.com/attachment.php?attachmentid=307639&d=1321990054
Fig. 10: the Trireme is not blocked by the Warrior.
http://forums.civfanatics.com/attachment.php?attachmentid=307640&d=1321990054
Fig. 11: the embarked unit is blocked by the Crossbowman.
http://forums.civfanatics.com/attachment.php?attachmentid=307635&stc=1&d=1321989715
Fig. 11b: a knight can kill a warrior while passing through another unit's zoc, and still continue moving
http://forums.civfanatics.com/attachment.php?attachmentid=308247&d=1321858479





Dealing with the Zone Of Control

The ZOC rule has an impact when you're moving units (to attack or defend) and when the enemies are doing so.
From a tactical point of view you may take advantage of the ZOC rule in some defensive situations, as explained below.

Tactical overview


the ZOC rule only affects adjacent enemies: thus, an attacking unit entering a ZOC is NOT stopped (unless this move is done within another ZOC). This is a key point to keep in mind when defending.
a unit may always move at least one tile in a turn (unless it is totally surrounded by enemies or obstacles).
the utility of a ZOC decreases with the enemy's mobility:

slow units (2 MPs) are mostly blocked by the ZOC
as of 3 MPs, units may flank the enemy, i.e. exit a ZOC, reenter it and still be able to move one more tile within the ZOC to attack on the side! (see Fig. 4)
fast units (> 4 MPs) may just be slowed down by the ZOC and can reach all tiles within the ZOC in the same turn (e.g. tanks on clear terrain or caravels on water).



remarks:
roads and railroads increase unit mobility, so a slow unit on a road may also flank adjacent enemies! (like a Horseman on clear terrain)
conversely, rough terrain generally slows the enemy and may in some situations prevent mobile units from flanking your units.
poorly spaced units may be fatal in defense because mobile enemies may zigzag between your units, exiting one ZOC and entering the next one several times, avoiding any movement penalty!
the ZOC rule is more effective at the beginning of the game because early units are generally slow. The rule has less impact in the modern age, when you're dealing with units like Tanks or Destroyers.


Determining the ZOC impact on your units

In some situations the impact of the ZOC rule may not be obvious.
Fortunately, the game may help you, as shown in the next figure with a Tank.
First select the unit and then click on the "Move Mode" button: the possible unit movements are displayed in blue and the enemies that can be attacked are circled in red.

http://forums.civfanatics.com/attachment.php?attachmentid=307829&stc=1&d=1322221577

Defending with the ZOC rule

The ZOC of your units also has an impact on the enemy and may be used for defensive purposes during the other players' turn.
But the computer won't help you here! You'll have to figure out for yourself how your units may block the enemies next turn.
To show the issue, two concrete situations are presented: the protection of ranged units and of embarked units.


Protecting ranged units

As shown in Fig. 14, the ZOC rule may be very effective against a slow unit like a Pikeman (2 MPs) because it adds 4 safe tiles for the defending units (in light blue).
This can be used to defend a city with Archers, or similarly to protect ranged units on clear terrain behind a melee unit.

The following conditions are essential:
your city or melee unit has to be adjacent to the enemy
the enemy should not be able to flank your units. That's why it does NOT generally work against mobile units like Horsemen, unless you have assistance from rough terrain. A typical pitfall is shown in Fig. 15.

http://forums.civfanatics.com/attachment.php?attachmentid=307656&stc=1&d=1322000795
http://forums.civfanatics.com/attachment.php?attachmentid=307648&stc=1&d=1321991814

http://forums.civfanatics.com/attachment.php?attachmentid=307623&stc=1&d=1321986638
Poor naval defense.

Trying to protect embarked units

If you're playing with the Gods & Kings expansion of Civ V it is not a real issue to protect embarked units because it is possible to stack them with naval military units. It's much more of a challenge to protect embarked units without this expansion, for the following reasons:

with the exception of the Trireme, naval units are very mobile. Ships have 4-8 MPs (without bonuses). And each water tile only costs 1 MP.
most naval units have a very short line of sight (2 tiles) so that they mostly cannot see the threat. Caravels have a line of sight of 4 tiles and may be used as naval scouts.
embarked units have no ZOC and are vulnerable; they cannot engage in combat at sea. An enemy ship only needs to enter an embarked unit's tile to kill it!

The invasion attempt on the right illustrates the issue. The French embarked units are to be protected by some warships and the set up looks at first sight pretty good:

the safe invasion corridor is delineated in green.
the ZOCs of the French ships are delineated in red.
the yellow arrows show potential enemy intrusions blocked by the French ZOCs.
(remember: an enemy may enter a ZOC and then still move one tile within it!)


In fact, the corridor is NOT safe at all, because some important paths were omitted. The red arrows show possible path of attack for enemy Destroyers (8+ MPs), zigzagging through the ZOCs and reaching an embarked unit. Each ship may then continue its movement but, fortunately, can only kill one embarked unit per turn. Otherwise all of the embarked units may have been destroyed!


The reason for this disaster-in-waiting is that the ships are too poorly spaced. In such a situation you'll need one more ship to protect the embarked units.
But spacing ships only by one tile is very expensive. That's why it's almost impossible to fully protect embarked units far off shore, and you will have to either deal with some losses, or scout the enemy navy so you know where to concentrate your defenses.
And do not hope the AI will not find the deadly paths, because the computer is much more skilled than humans at path finding!





Known Issues

There is currently a bug for units with movement points beyond their natural limit (Danish units disembarking or Persian units on the turn a golden age ends): when they pass through a ZOC or over a river, they do not expend all remaining MPs.
Following spoiler explains the bug in details.

http://forums.civfanatics.com/attachment.php?attachmentid=308270&stc=1&d=1319476040

Danish unit exploiting bug in excess movement points

Units with movement points beyond their natural limit expend the max movement points rather than their full when they cross a ZOC or a river.
As shown above, a Danish Rifleman may disembark and be at 4/2 movement points available, and at that point crossing a ZOC will expend only two movement points, leaving them able to move up to two more tiles.





Conclusion

By limiting the enemy's movements, the ZOC rule is very useful to protect weak units like ranged or embarked ones.
But the rule may have unexpected results: depending on the enemy mobility (and on the terrain), you may protect your rear and side units well, only your rear units, or none of them!

As a rule of thumb: beware of Knights! beware of Caravels!





Patch version of this article: 1.0.1.383

Image uploads

More images

And another image :).

http://forums.civfanatics.com/attachment.php?attachmentid=308247&d=1321858479

Very good article. Thank you for taking the time!

Interesting bit about the embarked units. Thanks for the time. A great deal of strategy is required for protecting embarked units with naval units and it's very nice to see a nice article like this explaining.

Awesome exposition! Thank you very much!

Excellent thread! I didn't know exiting and entering didn't count. I applaud the liberal use of images to illustrate the concepts involved.

Great article! I wish you and the other writers here would re-do the entire Civilopedia.

Great article, I've learned a lot. But I have a question.

Embarked combat units do NOT exert a ZOC.

Does this rule also apply to embarked combat units of the Songhai?

Great article, I've learned a lot. But I have a question.



Does this rule also apply to embarked combat units of the Songhai?

I believe it does. Songhai units (and embarked Conquistadores) have the special ability that they can't be insta-killed by overrun, but they still can't attack. ZOC is only exerted by units that can attack.

yikes, this can get messy.

thank you for such detail. i'll think a lot more about unit movement and spacing.

Wow... that's gotta be covering everything, well done :xmas:

well done on a well illostrated thread very good work

Good Work :thumbsup:

Ok I still am not getting this zone of control thing, in the following image (I'm rome, fighting against spain), my archer on the horse tile should in theory be protected by the Legion's ZoC; the spanish warrior must move through two squares protected by the legion in order to get to my archer.

http://i.imgur.com/mC0Ms.jpg

Yet on the next turn, the warrior runs straight through and kills the archer in 1 hit. Why does the ZoC not work in this case?

The first move by the warrior is not entirely within the Legion's ZoC. The ZoC only deals with movements made entirely within it. Thus the warrior uses one movement point by moving from a tile outside of the ZoC to a tile within the ZoC, but then is still able to move, because the first move was not entirely within the ZoC. If the enemy archer were a melee unit, it would not be able to attack your archer, because it moving to the tile one east would be a move from a tile within the ZoC to another tile within the ZoC, which uses up all movement points.

So, from the article:
Only direct moves within the (same) ZOC are affected (red arrows)
Other moves are NOT affected. In particular the rule does NOT apply:
if an enemy enters or exits the ZOC (blue arrow)
if an enemy exits the ZOC and at the same time enters another ZOC (green arrow)
if an enemy exits the ZOC and reenters it later (yellow arrow)

Likewise, you would be able to move your archer to the marsh tile one east of the warrior via the tile one east of the enemy archer, because that first move is not conducted entirely within a ZoC. You are entering a ZoC, not moving within one. Your Legion, on the other hand, would not be able to move to that marsh tile, because its first move would be within the enemy archer's ZoC.

Hope that clears it up. :)

The ZOC rule limits the movement of units that are adjacent to enemy units

this is a key point: the spanish warrior is NOT adjacent to your Legion, so it can enter the ZOC (ZOC rule does NOT apply, yet) and then still move one tile within it, killing the archer!
The spanish archer is blocked by the Legion's ZOC but it does not help :)

if your legion killed the spanish archer on the hill, it would then be protecting your archer from that warrior.

Cool I get it now thanks heaps guys! I feel a little derpy now cause rereading the original post explains it pretty well.

I don't get why my warrior was able to move like shown in this picture:

http://forums.civfanatics.com/attachment.php?attachmentid=312639&stc=1&d=1328028229

Were you at war with Bismarck?

Hmm, no I wasn't. Thought the ZoC rules always applied... but I guess that just seemed to be the case because barbarians always annoy you with their ZoCs right from the start of a game.

I didn't even know there WAS a ZOC! This game is much more complex than I thought... :love:

I noticed the Danish unit disembarking exploit before, and never knew exactly what was going on. After reading this and seeing that the unit actually has double it's maximum MPs, I can see that the problem is mathematical: ZOC uses up the unit's LISTED LIMIT of MPs, not its REMAINING MPs. The programmer didn't count on units being able to have a higher number of MPs than their listed limit, and because of this, made ZOC consume the normal limit's worth of MPs, which doesn't stop a unit that has higher than 100% of its MP limit.

In this case, the Danish Rifleman, with 4/2 MPs, loses 2MP for ZOC and not the 4MP. Had they counted on a unit being able to have greater than its maximum, they could have simply programmed ZOC to use up all actual remaining MPs (left-hand value of MPs) rather than the unit's normal limit (right-hand value). Obviously, they just never counted on this occurrence, and because Denmark was in a DLC, I think that maybe they didn't test the ZOC rules with regard to the UA they programmed for Denmark.

Very interesting.

Bonjour,

I reread the article to check if it is still valid for G&K.
As the ZOC rule did not change, I changed only the following details in order for the article to be valid for G&K, too:

- Fig. 5: changed caravel to Battleship (caravels have only 4MP in G&K !)

- Trying to protect embarked units

If you're playing with the Gods & Kings expansion of Civ V it is not a real issue to protect embarked units because it is possible to stack them with naval military units. It's much more of a challenge to protect embarked units without this expansion, for the following reasons:

You may correct my english...

Thank you so much for explaining that !!