Heatmap

The Heatmap is a mechanic that controls the spawn of zombies depending on the player's activities. It does not have a literal implication towards temperature but it does affect a certain area around the affected zone. It may be easier to think of this as a measurement of the activity level in a given area. The higher the activity level, the more likely zombies will appear.

Every chunk (a 16 X 16 block area ) has a heat level value and various activities can increase the heat level. Heat generated in a chunk affects that chunk and all adjacent chunks. Once the heat-generating activity stops, the heat level will decrease slowly over time.

Heat is accumulated on a 100.00% scale and will constantly increase and decrease.

To see the heat level of the chunk that the player is in, activate debug mode, and press F8 twice.

Effects of Heatmap
If the player performs certain activities in a small area, the heat of that area will increase. If the heat level is high enough, there is a chance that it will be set to around half of its value and a certain event will happen near the affected zone. The higher the heat of an area, the more likely that such an event will happen. 100.00 points will instantly reset the counter to 0.00.

Scouting Zombie
Formerly done by the Spider Zombie, scouting is now performed by Screamer, which after spawning, will wander to the affected area. If they spot a player in the area they will emit screams, which will then spawn random zombies around it, possibly even a horde if the screamers are not defeated fast enough.

Even if the screamer does not notice the player, it's always preferable to dispose of it quickly, because it will start summoning zombies by itself when it has scouted for too long and has decided to storm the player's heatmap-generating object instead.

Pitstop Horde
Pitstop hordes are similar to a wandering horde, but these only happen if the heatmap got reset too many times. Pitstop horde has varied difficulty and is dependent on the reset frequency and may even spawn Special Infected that may cause trouble for the player. Unlike the wandering horde, pitstop horde will walk directly toward the source of the heatmap, and will eventually seek to break the player's door and destroy the source whether it's the player's campfire, workbench, chemistry station, or much more. Pitstop horde event will never happen during the blood moon and may include screamers.

Things that Affect the Heatmap
Heat is generated in Discrete "packets" called heat events. Every heat event has a strength it contributes to the heat-map while it is alive and a lifetime which it will last. So if a player uses 2 campfires for 30 in-game minutes that would generate 2 events (as 30 minutes is only long enough for each campfire to make one event) each event would have a strength of 5 and so the heat for the chunk would be 10%.

Using Blocks
Using the following blocks will generate heat :

What do these numbers mean?

 * Strength: The Percentage of heat an event will contribute (when made from this block).
 * Frequency: The time,or Number of 'ticks', between heat event creations.
 * Lifetime: The time,or Number of 'ticks', until an event expires.

Note: The first heat event is generated immediately upon starting the activity, and the second event generated after the frequency timer has been reached.

Ticks
Block heat events use a unit called ticks to decide when to expire and stop contributing heat as well as blocks to generate them. 1000 ticks occur every in-game hour so the length of a tick in real time depends on game speed but at the default day length of 60 minuets per day a tick occurs every 3.75 seconds.

An example
According to the table above, each Forge generates 6 heat every in-game hour thus running at the default game speed 2.5 minutes. These heat events will stick around for 5 in-game hours meaning with 2 forges running constantly without any other heat sources after 2.5 in-game hours the chunk heat would be (6 [the heat strength] * 3 [number of events]) * 2 [the number of forges] = 36%. After 8 hours the maximum for each forge would have been reached (as for forges after 5000 ticks/5 in-game hours heat- events start expiring) and thus with reference to the table above 30%*2 = 60% total heat in the chunk. This maximum would be stable until new heat sources are added/ the forges turn off.

Dissipation
In the file Stealth.txt, heat map time is defined as "the time in seconds it takes for the heat to dissipate. Dissipation is not modelled, it's instant off after the time." However, it appears to be contradicted in blocks.xml by a comment which states "HeatMapTime decays in x seconds, and scales with game time" this comment is frequently misinterpreted to mean decay is modelled. It is NOT. Heat-events expire after a certain amount of time without any attenuation in between. This comment refers to torches, candles and burning barrels which follow a different rule set (see below), presumably for optimisation reasons as they are more common than the other heat-event producing blocks.

Flickering Fires
Flickering fires, that is Torches, candles and burning barrels, when placed by the player (i.e not as part of a prefab) produce heat events. However unlike other sources of heat events from blocks they do not emit in line with an interval. Instead they generate heat events simultaneously every real-world minute. This is likely for performance reasons. If they were emitting normally they would have a frequency of about 666 however this is difficult to measure and not of a huge amount of use. The more important fact to remember is that candles are half torches and barrels and so for places you expect to spend a lot of time (like bases) are preferable.

Example: In default game speed, 60 minute days, a single torch adds 0.5% heat every real-world minute. 10 torches would reach 100% after 20 real-world minutes. However, with 120 minute days a single torch adds 0.25% per real-world minute. 10 torches would reach 100% after 40 real-world minutes.

Generating maximum heat
If you are looking to purposely generate as much heat as possible, and draw the maximum amount of zombies to a specified area, then 25 campfires fully loaded with wood will consistently reach, and maintain the heat map at 100%, drawing extremely large amounts of screamers and thus zombies, once it reaches 100% you can turn 5 of them off, as you will no longer need the additional boost to maintain the heatmap at 100%. One should note that only 4 consistent campfires are needed to reach 100% heat every so often.

Starting auger 100 times will instantly spawn screamer. With averge auger RPM of 300, it allows to spawn 3 screamers per min

Using Items
Firearms and explosives generate heat on a per-use basis. Below is a collapsed Table of everything relating to using items that contributes to the heat map:

Crimes Against Nature
Felling one or two trees will affect nothing, but chopping down many trees within a small area will exponentially attract more zombies. Using loud tools like a chainsaw will also accumulate points toward the heatmap pool, same goes for mining too much and digging large holes.

Farming and gathering do not affect the heatmap.

Hunting; killing Animals using bows or other quiet weapons will not generate heat.

Metallic & Glass Objects
Dismantling with a wrench or damaging a metallic object using another metal tool increases the heatmap with each hit by 0.1 for 60 ticks. Using tools with higher block damage will result in less cumulative heat due to having to hit the object fewer times. Bashing open safes also increases the heatmap, but at an even higher rate due to the high durability of safes. Lockpicking safes is safe from the heatmap.

Damage done to metallic objects by zombies will also increase the heatmap; therefore scrap and steel structures, while more resilient, may end up drawing more zombies than the player can deal with. This leads to some players building a more flimsy outer wall to prevent wandering zombies from hitting strong defences which are often made of louder materials.

Upgrading and constructing using metals will also increase the heatmap. This counts for building scrap blocks and upgrading blocks and doors to their metallic tiers.

Metal Traps such as the spinning blade, log iron spike, and barbed wires will generate heatmap as they take damage from zombies and players alike.

Breaking blocks
Below is a table of materials and their heat stats if broken (Note that whist these stats are correct for the sounds breaking most objects calls the sound twice meaning in reality most of the values should be doubled):

Horde Mentality
This is another problem that some players may encounter, usually those who chose to shelter in only one place. Even if no heatmap-generating actions are done around this place, zombies may still spawn and approach the player. The heatmap would just progressively increase more and more rapidly over time. While it is possible that zombies, as a collective, take note of where the player usually hangs around as they keep trying to get to the player, this may also be part of the compounding effect where zombies being killed generates heat, which spawns in more zombies, and then the spawned zombies are killed, and so on. This has become much less of a risk in recent versions so long as there is no excessive use of guns when dealing with zombies at the base (other than on blood moons).

Other Actions

 * Riding Bike - While not easily noticeable, the minibike does generate heat when driven around, but it does not necessarily attract zombies' direct attention.
 * Doors - Opening or closing doors/hatches upgraded with metal increases the heatmap by 0.05 points each use.

What Does NOT Increase the Heatmap

 * Running - It does not increase the heatmap, but will still generate noise that may attract nearby zombies.
 * Non-Fire based light sources, such as spotlights.
 * The use of Generator, Battery, and Solar Bank will not increase heat passively even when being used (though a very very very small amount is generated when opening them)
 * Player bed also does not contribute to the heatmap anymore
 * Speaker - While this also might be a bug, not only do speakers not generate any heat, they do not attract or even redirect zombies near it.
 * Smell - While smell does attract nearby zombies via a separate mechanic, carrying an item which smells will not alter the heatmap. (Smell mechanics have been disabled since A16.3 due to problems)

Compounding Effects
Each individual item or action affecting the heatmap adds to the heat level. Thus multiple Campfires or forges compound the increase in heat for a given area. Also, a single item's generated heat levels are compounded over time. A single campfire used for a long duration will eventually build a high level of heat.

Because it takes time for heat levels to naturally decrease and because the action of fighting zombies—especially with firearms and explosives—also generates heat, it is possible to get caught in a cycle in which screamers continue to spawn to investigate and attract additional zombies.