In today's exclusive Gamasutra feature, former EverQuest designer Kevin Carter reveals "three simple guidelines you can use to make your game worlds that much more believable, and therefore that much more exciting to play through", citing games from Half-Life to Out Of This World. In this excerpt, Carter explains why in designing a believable and immersive game world, it is imperative that developers begin by thinking about their game's non-player characters, taking care to make sure they fit within the context of their environment: “I’m going to use the term “ecology” very loosely here, so loosely that it need not necessarily apply to creatures that are alive in the strictest biological sense. In other words, and this disclaimer is really only necessary in a discussion of video game world building theory, the ecological patterns I’m about to describe can apply to creatures that are not specifically alive, creatures such as undead zombies, self-replicating robots, puddles of sentient ooze... or whatever other imaginative aberrations your particular game may place between the hero and the much-feared main boss! In any case, regardless of your particular brand of bad guy, you should always remember two things. 1) creatures are part of their environments and, as an ancillary rule, 2) creatures shape, and are shaped by, their environments. What I mean here is that creatures do not exist in a vacuum. When a player encounters a creature in a game world, that creature should, at a glance, appear to belong in its environment. Communicating, or at least implying, the connection between a creature and its environment is often far easier then most game designers realize. There are several ways to do this including: environmental associations, contextual events, or even simply the visual appearance of the NPC model itself. The easiest of the tools that can be used to tie creatures into their world come from environmental associations between the creature and the surrounding game geometry. In other words, wherever a creature appears in game, there should be nearby an object (or objects) typically associated with that creature type.” You can read the complete feature here, with more insights from Carter on what he feels are essential elements to be considered in developing convincing virtual worlds (no registration required, please feel free to link to this column from external websites).