The words procedurally generated spark the idea of endlessly interchangeable combinations of parts linked together in hundreds of different ways, creating something unique that may never be seen again. At its heart, that’s not terribly far off the mark, but as Firaxis Games discovered during the production of its 2012 reboot, XCOM: Enemy Unknown, there’s a gulf between random and procedural. And traveling from Enemy Unknown to XCOM 2

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“ Random's not fun. That is the lesson we learned.

Building A Better Tomorrow

“ Buildings aren’t procedurally generated, but crafted set pieces, and almost entirely destructible.

Your Mission, Should You Choose To Accept It

The first rule, according to XCOM 2 Art Director Greg Foertsch, is striking a balance. “Random’s not fun,” Foertsch declared. “That’s the lesson we learned. The procedurally generated levels in Enemy Unknown, they were more random.”It’s the kind of randomness where each slab of cover could be a bench, or a trashcan, or dumpster, or some clumsily lain obstacle course of the aforementioned parts that don’t give you good opportunities to advance your soldiers under fire. “Maybe that was a bridge too far.... And, visually, it also looks terrible.”And so Firaxis turned to hand-crafted maps for Enemy Unknown that both looked good and played well. But the other side of that coin is that because each piece was meticulously constructed, Firaxis could make only so many – the finite number of maps just wasn’t enough to sustain the series’ dedicated and diehard fanbase, who very quickly learned to anticipate enemy placement.“Overwhelmingly, players of [Enemy Unknown] said, ‘We like the maps, but man...we're exhausting them pretty quick,’ even though the team put in 80-plus maps,” said Garth DeAngelis, lead producer on both Enemy Unknown and XCOM 2. “And they were all handcrafted, which was a ton of work.‘So,’ we said, ‘How do we resolve this problem?’” The answer is what the team literally calls “the plot and parcel system,” and what DeAngelis refers to as “a big quilt.”Here’s how the metaphor works: imagine a map in XCOM 2 as a quilt, with holes where a pre-constructed modular building will be placed – those are the parcels. The holes are big, small, and medium-sized, with a range of unique buildings that could fit into each size. These buildings, and the holes in which they’re socketed, are the parcels of the system.However, with the addition of mod support in XCOM 2 -- which we’ll be diving into next week -- and the modular nature of building design and creation, there’s no telling how many different variations and original buildings you’ll soon be blowing holes through. But in the meantime, Firaxis is planning plenty of variety in each map layout.“You might get a gas station next to a park, next to a parking lot in one playthrough, and that's your experience,” DeAngelis said. “Even though the ‘quilt’ is the same, all of these elements are procedural, mini set piece bases.”The plot portion of that system comes into play in the space between our buildings. At the risk of mixing our metaphors, think of the plots as the connective tissue that links one parcel to the next. The plots could be a street, or a park area, or train tracks, or a river bed, or an empty tract of land, et cetera. When you begin a mission, the map reaches into a bank of options and fills it up.“All the stuff you see that comes up on the road, like where the cars are, the lights – that's all random rule,” Foertsch said. “It has a pool of things it can put there. But we think more about it as like a little bit of a diorama set than, ‘I'm going to put an individual trash can here.’”“In addition, the connective tissue does have random cover that propagates on top of it,” DeAngelis continued. “So, cars in the streets, where telephone booths are, where the security checkpoints you saw in the announce trailer are, those come in as well.”Each chunk of each plot will be procedurally generated from an appropriately themed bank of around 20-ish possible dioramas, and so on so forth. This is how XCOM 2 will generate a near-endless supply of maps, and how you’ll likely never play the same one twice.But the procedurally generated approach of XCOM 2 doesn’t stop with the patchwork environments and battlefield locales. For the first time, your squad will not only be tasked with exterminating the aliens in the area, but secondary mission objectives which will cater to the procedurally generated settings.“It might be blowing up one of these buildings to spark the resistance,” Foertsch said. “It might be hacking a workstation, or protecting a device. All these different things you can do that can show up and in dozens of different buildings and areas. And you don't know what you're going to get.“We're really excited about the baseline gameplay. Because it just ramps up that whole procedural factor beyond just geometries in a different place – which is what we wanted to set out to do.”“I'm super excited about this,” said DeAngelis. “There was an interesting long-term learning lesson. Because again, with the pie-in-the-sky approach, you're like, ‘Let's make it as random as possible so you truly get play forever and totally randomized.’ But there's so much value in what the artists and designers do with crafting, so it's really that nice hybridization of techniques we learned in Enemy Unknown, but then try and give back some of that UFO Defense.”

Brandin Tyrrel is IGN's procedurally generated Associate Editor. You can find him on Twitter