Scrollin', Scrollin', Scrollin'

When playing a game, it is very important to the player what he/she can see on the screen. Being killed by an off-screen enemy is frustrating, but trying to force an entire game level onto one screen can be impractical. While older games had only one screen's worth of data, which as a result was visible at all times, game worlds gradually began growing beyond the confines of the screen.

In 2D games, the most basic solution is to scroll the screen - horizontal scrolling was the most common (especially among platformers), but vertical and multidirectional scrolling were also used. In scrolling games, on-screen context determined everything. Often, enemies or goals were only processed by the game while on-screen, allowing the player and program to forget about faraway objects. With a world following the player character and only revealed one screen's-width at a time, things frequently moved in and out of scope, keeping the game interesting and allowing for the creation of much larger worlds than in single-screen games.

As games entered 3D, scrolling was no longer possible, but the player's field of vision is still only limited to what's happening on-screen. This made the rendering of active off-screen space even more important than in 2D games - where passive off-screen space was quite common - as there was always area around and behind the player that could affect gameplay but could not be seen. Rather than have objects go out of scope as soon as they are off the screen, the game remembers where they are and still allows them to act. There are limits on off-screen processing, though: some games have such large worlds that the console simply cannot continually process the entirety of the map at all times. Games like Grand Theft Auto solved this problem by using distance - the game only renders objects a certain virtual distance away from the player character. In a sense, this is almost like a 3D equivalent to scrolling, in which the 2D screen will only reveal objects a screen's width away from the player.

What are some ways, other than scrolling, that you have seen games use to gradually reveal a larger world? (i.e. loading screens, single-screen rooms, etc.)