Horizon: Zero Dawn looks incredible- it’s actually shocking how good the game looks, because where previous PlayStation games have looked this good, they have also always been linear corridors, such as Uncharted or Killzone. But Horizon is a vast, open world, fully available for the player at all times, and it maintains this level of visual fidelity.
One way that the game might be doing this could be the new GPU based runtime technology that Guerrilla are using with the game. This technology procedurally generates the visual environments around the player, meaning that not just the trees and rocks, but the entire world and the wildlife within it, is dynamically created by the GPU. Do note that this is not procedural generation like No Man’s Sky did it- the world will still very much be handcrafted here. This is just discussing how the GPU handles the rendering of the world.
Guerrilla Games’ Senior Tech Programmer, Jaap van Muijden, will talk about this new procedural placement system during a programming session at the Game Developers Conference 2017, so we should hopefully learn more about how exactly Horizon gets to have its cake and eat it too then.