Cityscape Fighting (Apocalypse)

Cityscape actions within Xcom Apocalypse. Analysis of battlescape missions is here: Tactical Missions

Alien Infiltration

A UFO will hover over a building and attempt to insert aliens via a 'grey smokey tube'. If an X-Com Base is hidden in the basement of that building, a Base Defense mission will immediately commence.

A UFO will hover over a building and drop blue particles with the sole purpose of scanning the building for an X-Com Base. If a base is detected, Alien Search styled missions will now have a single UFO initiate an X-Com Base Attack mission and the others present in the group will continue searching (dropping their 'blue rain' over random buildings). If multple bases are known, only one will be targeted for infiltration per Alien Search mission - and further Alien Search missions will be NOT suspended. Alien Search missions will still be scheduled like normal irrelevant if one or many bases are known.
Note: The blue particle effect was typically called "Micronoid Rain". (see "Note", below)
X-Com may initiate a search by having X-Com agents at a building (or in a vehicle at the building) by selecting "Search". If an alien presence is detected, a battlescape mission will commence. If no aliens, the organisation will file a protest by becoming very slightly more hostile.

Bombing Buildings

Hostiles will target a building with their craft and attack it with the purpose of destroying it. If the building is above a hidden X-Com base, and if the topside structure sustains massive damage, it can destroy the base underneath. That is: if a great portion of the building is destroyed or if the home cell is destroyed, the X-Com base is destroyed also.

Attack

Any building can be attacked by anyone with vehicles to cause collapse and financial loss. X-Com can target ("Attack Building" button) any building for destruction, including (using manual vehicle control) any non-building infrastructure such as people tubes, trees and parklands, city walls, roads, and any pillars or supports .
Government funding for the new week is assessed by the total score. City damage is usually the largest contributing factor for reduced funding, and may become excessively negative when damage is caused by fighting alien crafts.

Damage

Any damage of the cityscape attributed to X-Com or Aliens, but not other Mega-Primus organisations, will be noted immediately in the Performance Log information window as "Damage To City" ...always a negative number!
Cityscape buildings have differing damage tolerances which depends on its construction.
Any building hit by a weapon, the tile impacted will either be destroyed, or not. Damage is not cumulative. If destroyed, the section directly above the now missing tile will collapse in a pan-cake fashion, and in severe cases, will lead to a chain-reaction destruction of adjacent sections until the whole building is a pile of rubble. Slums, being derelict buildings, are structurally weak and prone to catastrophic collapse from even the weakest weapons. Severe destruction of a structure may disable the building as a viable destination for battlescape missions until (partially) rebuilt, however, destruction of the home cell will immediately disable the building. X-Com base locations are best chosen to be under Warehouse styled structures due to their resistance to damage.

Defense

If any building has been impacted by a weapon (even accidently), the owner will become slightly more hostile to the organisation which caused the damage. Further 'accidental' impacts will quickly anger the company. If a building is under sustained attack (message bar: "...building under attack by..."), the building's owner will launch craft (if available) to defend the building and destroy any ~~attacking~~ hostile air or road vehicles in the vicinity.
Note: Any impact is regarded as an attack. It does not need to destroy a tile or collapse the building. These accidental impacts can be used to turn two friendly (with each other) organisations into two hostiles. eg:

Attack a building owned by one (hostile to X-Com) organisation until defenders are launched or attack an escort-roleΔ UFO to attract its attention.
Lead the craft(s) (use evasive attitude) to a building which is owned by the friend of the organisation which currently chasing your vehicle.
Loiter around their friend's building at a low to medium altitude in a location that will not damage your craft if parts of the building collapse, but will allow the hostile-to-you craft's missed weapon shots to impact their friend's structure.
Wait (stationary or do short random movements with your air craft) around the building. Your attackers will shoot at your vehicle but may end up missing, hitting their friend's building enough times that their 'friend' (now hostile) launches craft to defend the building. If that message appears (mentioned above) but no craft have been launched, it does not matter. They are now hostile to the organisation which caused all that damage!
The company that caused the damage will not be hostile to their 'old mates' until they start to be attacked by their former friend. The two, once friendly organisations are now hostile to each other!

This bait and dodge tactic can be used to change relationships. Aliens can be forced to be hostile to anyone (including Cult Of Sirius), Transtellar can switch back to be able to transfer equipment again if they are hostile to aliens, resuming the purchase of goods from hostile companies etc. and any inter-organisation relationships can be soured just because!

Relations work on a simple principle: the enemy of my enemy is my friend. If X-com attacks one organisation, any hostile companies to the victim will like X-Com more, whereas friendlies of the victim will hate X-Com.

Δ The named UFO: Escort does not have offensive weaponry.

Consequences

Only weapon impacts from either X-Com or Aliens will influence your 'Damage To City' score, that is, negative score is 'awarded' for each impact. What happens after that impact is irrelevant.
X-Com's score will not be affected by:

Illegal flyers and police action.
Organisations hostile to each other fighting in the cityscape.

Special Note: funding does not matter, see above: Raid:The Mechanics.

Illegal Flyer

Any organisation (including X-COM) can attack any building with vehicles. An alert is generated (if enabled) when other organisations send out craft, hence, "Illegal Flyer detected". X-COM intervention is not warranted unless the building is above your base. Score is not affected unless X-COM is involved.

Illegal flyer attacks launched by computer-controlled organizations normally consist of two vehicles, selected from the organisation's vehicle park according to the following priority list: 1. Police Hovercar; 2. Phoenix Hovercar; 3. Hoverbike; 4. Valkyrie Interceptor; 5. Hawk Air Warrior. However, one vehicle of each type, if available, will always remain in the vehicle park.
Example #1: if the organisation has 2 Phoenix Hovercars, 1 Hoverbike and 2 Valkyrie Interceptors available, the attack will consist of 1 Hovercar and 1 Valkyrie.
Example #2: if the organisation has 1 Phoenix Hovercar, 5 Hoverbikes and 2 Hawk Air Warriors available, the attack will consist of 2 Hoverbikes.

Megapol's Police Hovercars do not trigger the "Illegal Flyer" alert, presumably since their actions are justified as in "upholding the law". However, a Valkyrie or Hawk sent by Megapol will trigger the alert.

The organisation that owns the attacked building will scramble flying vehicles to defend its asset. These will usually swiftly overwhelm and destroy the attackers.

Raids

Organizations unfriendly or outright hostile to each another may conduct actions as listed in the Message Bar as either "raided by" or "stormed by" or "attacked by". This has no relevance to X-Com.
If a building targeted for a raid contains a hidden X-Com Base, a Base Defense mission will occur.
A raid of a building cannot be avoided in any way since it is a scheduled event and the player has no indication that one will occur. Hostile vehicles arriving at a building is a random event and has no relevance to the possiblity of future enemy action, hence, destroying hostile company vehicles does not influence the schedule.

Overspawn Drop

The aliens focus more on destruction instead of infiltration. Motherships will drop a single Overspawn each onto Mega-Primus with the intent of massive damage and destruction of its buildings, roads and infrastructure.

Apocalypse Mission

When X-COM destroys the Control Chamber in the Alien Dimension, it eliminates the Alien's ability to grow new UFOs. The alien horde now realise their imminent defeat... with a final act of desperation by sending the remnants of their fleet to Mega-Primus. All remaining UFOs in the alien dimension (except probes) will swarm into Mega-Primus on the next scheduled mission, to destroy the whole city. With the critically important Control Chamber destroyed and no more UFOs to infiltrate Mega Primus, the alien's ultimate objective of sustaining the Micronoid lifeforms with human hosts has essentially failed.

Note

In times past, a common misconception was that Aliens could perform a "subversion" of an organisation via the "Micronoid Rain" effect. It was believed that such action of the UFO above the target organisation's building would immediately infect the inhabitants with Micronoids (hence "Micronoid Rain") and result in immediate 100% infiltration. This micronoid rain definition was proven to be incorrect. The purpose of the UFO and its 'rain' is to scan the building for an X-Com base (for future elimination). (see "Alien Search", above).