Fallout 3 and the Illusion of Open Level Design

I've been playing Fallout 3 for the past month and I'm very pleased with it overall. However, after playing for sometime I decided to explore the edges of the map and when it appeared that I could continue onward I was met with an invisible wall along with text stating that I could not continue any further. Now, this is not necessarily a bad thing. In fact, I recall that Oblivion had almost the same message when reaching the edge of the map. Does this break the illusion of the vast open world that Fallout boasts of? Well, maybe just a little.

This is not a problem that is not particular to Fallout however and it urged me to think about how level designers are always forced to impose physical limits on the player. The ability to poke and prod the player into the right direction, while keeping them on track is a related problem, but here I want to specifically discuss how to limit the player to remain in a finite space with the illusion that they are actually part of a much bigger world. Specifically, the only games effected by this are those in which the player is an active participant in an ever-changing world, so any open-world type of game will do. It is specifically within these styles of game that it is ever important to maintain this illusion of a large, unconstrained world.

So what are some of the strategies that have been or could be used to confine players within this type of game environment? Here are a few:

• Invisible Walls - This is probably one of the least imaginative ways to let players know that they have reached the boundaries of the game world. This is the design that was chosen for Fallout 3 and Oblivion and simply tells the player they must turn around.
• Geography - A more natural limitation is to design the world geography in such a way that it is physically impossible to continue. This could be the addition of mountain ranges or an island setting with an endless ocean (Morrowind,GTA) that is impossible for the player to traverse.
• Design Enforced - This is similar to geography in that it places barriers that the player cannot physically cross, but which are in line with the theme of the game. For instance in Assassin's Creed, the player's screen is garbled at the edges of the map in accordance with the virtual reality theme of that game. This could also includes a death barrier, such as a radiation field that kills the player if he continue past the boundaries, thus making it impossible to continue. I would also include architecture based limitations as well, such as the ruined cities in games such as Gears of War.
  

In most types of games, it's a given that the world is finite, but it is up to the game designer to at least provide the illusion that the world is larger than it seems. While it may not completely invalidate the game experience if a poor decision is made when placing barriers around the game world, it can be a jarring moment for the player when they come across something that is out of place or blatantly obvious. I'm definitely going to be keeping my eye out for other ways that games attempt to do this as play in the future.