Bases (Apocalypse)
Bases are the most important asset that a commander of X-COM can possess. Bases are where extra weapons, ammunition and armor are stored for your troops. It's also where captured aliens and artifacts recovered from crashed UFOs are researched to allow new and deadly forms of warfare. It's where ships that were damaged in the battles with the alien space ships are repaired and equipped. It is also where you construct monstrous ships of awe-inspiring power and create armor of startling strength.
Base Layout
The bases on Apocalypse have predefined areas where it is possible to build new facilities, all linked by corridors. It is impossible however to expand the base more than the already excavated areas, which can limit the usefulness of a base.
The game starts with X-COM already in possession of a base, and if needed, the Government can be contacted to give additional base(s), provided the funds are available. The layout of those new bases can vary, so it is prudent to check the structure before any purchase.
Buying A New Base
There are 4 factors to consider when buying a new base: Area, Cost, Layout, Building Type and Location. A complete list of all the buildings and their characteristics can be found at Base Locations and a detailed analysis of their layouts at Base Layouts.
Another important factor when buying a new base is the number of launch tubes for aircraft that the building possesses. The more it has, the faster multiple X-COM craft will scramble to intercept any UFO or hostile craft, although this can also be achieved by placing craft into the buildings of other Organizations, especially the Space Port.
Base Location and Type
Since X-COM will be using mostly air vehicles the location of the base isn't that important since aircraft can reach quickly any part of Mega-Primus.
More important is the type of building where the base is located. All bases are either Warehouses or Slums. While this has no effect during Base Defense missions since they will be fought using the base layout, it can be of extreme importance during the Cityscape Fighting.
Warehouses are more tougher than Slums when taking a hit from craft weapons and their profile is lower, making them harder to be hit by a stray shot. Slums cost about the same as Warehouses but the structural integrity of these badly undermaintained structures is very questionable. If the square containing the craft/agents is hit and it falls down all of the agents present at that base will be killed, and any craft present will be destroyed. However Slums are usually the only kind of buildings purchaseable in distant areas of the city.
Base Design
Bases with large layouts are able to have more items constructed in them, and can make good all-purpose bases. Bases with limited or contorted space needs to be specialized as a specific type of base, such as one which only repairs your vehicles, or only researches Quantum Physics or Biochemistry, or only contains Workshops.
A few Living Quarters and a Stores module, are always necessary. If any base is attacked by an organization, it is necessary to have at least one soldier at the base otherwise X-COM's opponents will destroy the base without opposition. In additions, any [[Workshop (Apocalypse)|Workshops] will also require storage modules in order to store the items which you just manufactured.
When planning your base, it should be noted that Repair Bays and Access Lifts are able to be infiltrated by hostile forces. If X-COM bases ever come under attack, these are the areas where the enemy will most likely enter from. To counter this, it can help to cordon off these sections with a small string of Security Stations, be they the advanced or regular form. This usually means that the enemy will take heavy casualties before defending agents run into them, and, in case the stations fall, the enemy will be down most of its assault force.
Finally, it is possible to transfer people between bases. If all the scientists and men are present in one base, it is very likely that one well-placed missile or beam can completely annihilate an entire platoon of troops and all your researchers, which would be a catastrophe. For this to happen a piece of building needs to falls on top of the bay through which X-COM agents enter and leave via car. Otherwise, the aliens can destroy the entire base without any casualties.