"Our problem was not unique, but our situation was: our world is very big yet it requires the same precision as a small one," the devs wrote in a blog post. "The team devoted to solving this decided to use navigation meshes. The serious problem it presented, though, was how to generate these meshes. With nearly two million objects on the map, doing it by hand would not be an option. So a method was devised to split the world up into grids, and then raycast at a precise interval and generate chunks of navmesh."
The result? Zombies that can figure out how to cross a street and go into a building without embarassing themselves. The team also talked about some of the livestock it's creating for the game, including carp to be fished out of ponds by survivors.