Thirteenth Floor was a memorable VR film in many ways - it was far deeper and darker than the Matrix, even though it came out the same year. It featured worldlets rather than worlds: It did not try to create virual worlds so much as virtual cities; sub-worlds complete and of themselves.

The denizens of these worldlets knew nothing of the limits of the world, although they were plain to see, if you drove far enough out.

What was nice about the method used in floor 13, was it did not cut off suddenly, like many if not most worldlets in modern times do. Usually you have a grid, of a set number of cells arranged into a square or rectangular shape. Up until the edge of that grid, everything seems normal, then suddenly all the trees, rocks, vegetation, man-made objects stop dead. If there is terrain such as rolling hills, it usually stops dead too. A wide featureless plain, or endless featureless ocean stretches out before the brave pioneer who makes it to the world's edge.

Striding out onto that plain, and looking back, one can see the island world, no-longer looking complete, but looking like an oddity, an abnormality - a place where the land rises and falls, rivers flow, birds chirp. A square island of life in a sea of nothingness.

It goes without saying, really, that such a view is unsettling. A better approach would be to wind the world down gradually, in stages. This, to a degree, preserves immersion, and then breaks it in stages, as you get near the edge.

The above scene, taken from Thirteenth Floor, shows exactly that concept.Rather than simply stop dead in its tracks at the edge of the prescribed world space, procedurally generated objects such as roads and telegraph poles, continue on into the distance, as does the terrain. It gradually loses all colour and texture, becoming simple wireframes. The sky likewise becomes a wireframe grid. At some point, likely just over the next rise, the wireframes begin to straighten out, and merge into that featureless plain. Or perhaps, an endlessly repeating texture, carrying on into infinity.

The transition is still hard - devastating if you believed the virtual world was physical, as in the case of the film, but it is not as abrupt as a complete drop-off to a sudden and very stark, eternal plain.

As a side-note, it is interesting that Thirteenth Floor's virtual worlds dissolved into green grids, and that trend was picked up by several modern virtual worlds. The screenshot below being from ActiveWorlds with cell visibility turned on.

This VR is one which meets the criteria of square worlds abandoned in an endless plain. As are most videogames, the virtual worlds Lively, Twinity, and Wizard, and likely many, many more besides.

Some videogames are starting to take up some of the lessons leared from Thirteenth Floor. The 2008 title Fallout 3 being one. Whilst this gameworld does have a square edge ultimately, players cannot access it without a half hour long walk outside the playable area. Instead, the rolling terrain continues unabated right to the end of the world, far beyond where any player might desire to go. Trying to cross it, only teleports you back about 200 yards.

Additionally, the trees, buildings, bridges, and ruined skyscrapers of this gameworld don't stop at the edge of the world, but continue on, beyond the playable area, until the rist rise is cleared. Then they stop. In this manner, immersion is preserved, even with a tiny worldlet a few miles to a side. Where 'playable area' is not possible, it would be worth giving serious thought to a Thirteenth Floor like approach - blend the scenery into the background over time. The world disappears bit by bit, rather than all at once. This gives participants the chance to turn back, before all is lost, and they are on that featureless plain.

References

The Thirteenth Floor

World Review: ActiveWorlds Gate 4.1

Further Reading

Resource List: Thirteenth Floor: Inspirational Film

Resource List: Fiction-Inspired Building Methods