The term "free roam" is also used, as is "sandbox" and "free-roaming". "Open world" and "free-roaming" suggest the absence of artificial barriers, in contrast to the invisible walls and loading screens that are common in linear level designs. The term "sandbox" is often used incorrectly. Open world doesn't necessarily mean sandbox. A true "sandbox" is where the player has tools to modify the world themselves and create how they play.
Generally open world games still enforce some restrictions in the game environment, either due to absolute technical limitations or in-game limitations (such as locked areas) imposed by a game's linearity.
Gameplay and design
An open world is a level or game designed as a nonlinear, vast open area with many ways to reach an objective. Some games are designed with both traditional and open world levels. An open world facilitates greater exploration than a series of smaller levels, or a level with more linear challenges. Reviewers have judged the quality of an open world based on whether there are interesting ways for the player to interact with the broader level when they ignore their main objective. Some games actually use real settings to model an open world, such as New York City.
A major design challenge is to balance the freedom of an open world with the structure of a dramatic storyline. Since players may perform actions that the game designer did not expect, the game's writers must find creative ways to impose a storyline on the player without interfering with their freedom. As such, games with open worlds will sometimes break the game's story into a series of missions, or have a much simpler storyline altogether. Other games instead offer side-missions to the player that do not disrupt the main storyline. Most open world games make the character a blank slate that players can project their own thoughts onto, although several games such as Landstalker: The Treasures of King Nole offer more character development and dialog. Writing in 2005, David Braben described the narrative structure of current videogames as "little different to the stories of those Harold Lloyd films of the 1920s", and considered genuinely open-ended stories to be the "Holy Grail we are looking for in fifth generation gaming".
Games with open worlds typically give players infinite lives or continues, although games like Blaster Master force the player to start from the beginning should they die too many times. There is also a risk that players may get lost as they explore an open world; thus designers sometimes try to break the open world into manageable sections.
Procedural generation and emergence
Procedural generation refers to content generated algorithmically rather than manually, and is often used to generate game levels and other content. While procedural generation does not guarantee that a game or sequence of levels are nonlinear, it is an important factor in reducing game development time, and opens up avenues making it possible to generate larger and more or less unique seamless game worlds on the fly and using fewer resources. This kind of procedural generation is also called "worldbuilding", in which general rules are used to construct a believable world.
Most 4X and roguelike games make use of procedural generation to some extent to generate game levels. SpeedTree is an example of a developer-oriented tool used in the development of The Elder Scrolls IV: Oblivion and aimed at speeding up the level design process. Procedural generation also made it possible for the developers of Elite, David Braben and Ian Bell, to fit the entire game—including thousands of planets, dozens of trade commodities, multiple ship types and a plausible economic system—into less than 22 kilobytes of memory.
Emergence refers to complex situations in a video game that emerge (either expectedly or unexpectedly) from the interaction of relatively simple game mechanics. According to Peter Molyneux, emergent gameplay appears wherever a game has a good simulation system that allows players to play in the world and have it respond realistically to their actions. It is what made SimCity and The Sims compelling to players. Similarly, being able to freely interact with the city's inhabitants in Grand Theft Auto added an extra dimension to the series.
In recent years game designers have attempted to encourage emergent play by providing players with tools to expand games through their own actions. Examples include in-game web browsers in EVE Online and The Matrix Online; XML integration tools and programming languages in Second Life; shifting exchange rates in Entropia Universe; and the complex object-and-grammar system used to solve puzzles in Scribblenauts. Other examples of emergence include interactions between physics and artificial intelligence. One challenge that remains to be solved, however, is how to tell a compelling story using only emergent technology.
In an op-ed piece for BBC News, David Braben, co-creator of Elite, called truly open-ended game design "The Holy Grail" of modern video gaming, citing games like Elite and the Grand Theft Auto series as early steps in that direction. Peter Molyneux has also stated that he believes emergence (or emergent gameplay) is where video game development is headed in the future. He has attempted to implement open-world gameplay to a great extent in some of his games, particularly Black & White and Fable.
Early examples of free-roaming, non-linear worlds (with gradually increasing open-endedness) include Bosconian (1981), Time Pilot (1982), Panorama Toh (1983), Dragon Slayer (1984), Ginga Hyoryu Vifam (1984), Hydlide (1984), Tritorn (1984), Elite (1984), Star Luster (1985), Brain Breaker (1985), Metroid (1986), Dragon Quest (1986), and especially the original Legend of Zelda (1986).
Released in Japan in 1986, the first Legend of Zelda is considered an early example of open world. It featured on-foot exploration in a fully-scaled, continuous, open world. With nonlinear gameplay, it set the foundations for later action-adventure games like Metroid and role-playing video games like Final Fantasy, while influencing most modern games in general.
There were several early games that offered players the ability to explore an open world while driving a variety of ground vehicles. TX-1 (1983), The Battle-Road (1984) and Out Run (1986) were non-linear driving games that allowed the player to drive through multiple different paths that lead to different possible routes and final destinations. Turbo Esprit provided a 3D free-roaming city environment in 1986 and has been cited as a major influence on Grand Theft Auto. River City Ransom (1989) was an early sandbox brawler reminiscent of Grand Theft Auto. Another early open-world game reminiscent of GTA was Takeshi no Chōsenjō (Takeshi's Challenge), a 1986 Famicom game only released in Japan; it was an unusual game for its time, featuring free-roaming gameplay while, much like GTA, allowing players to randomly attack any people (and having to escape police if the player murders a person) or even punch random objects (including menus).  Another precursor was Speed Rumbler (1986), which featured a combination of run & gun shooter with driving mechanics, resulting in a new action game hybrid that would inspire games like Grand Theft Auto decades later.
Since 1991, the Metal Max series of post-apocalyptic role-playing games featured truly open-ended, non-linear gameplay. They lack a predetermined story path, but the player is instead given the choice of what missions to follow in whichever order while being able to visit any place in the game world at any time. The ending can be determined by the player, who can alter the ending through their actions, can complete the game at almost any time, and continue playing the game even after the ending. Some of the games give the player the freedom to complete the game almost immediately after starting it, particularly Metal Saga, which could be completed with a full ending scenario just minutes into the game, making it the shortest possible RPG. Since Romancing SaGa in 1992, the SaGa series has also been known for its truly open-ended, non-linear gameplay, offering many choices and allowing players to complete quests in any order, with the decision of whether or not to participate in any particular quest affecting the outcome of the storyline. The game also allowed players to choose from eight different characters, each with their own stories that start in different places and offer different outcomes. Romancing SaGa thus succeeded in providing a very different experience during each run through the game, something that even later sandbox RPGs such as Fable had promised but were unable to live up to.
Metal Max (1991) was an open-world RPG, where the player can pursue missions in any order, visit any place in the game world, determine the ending through their actions, complete the game at almost any time, and continue playing the game after the ending. Hunter (1991) has been described as the first sandbox game to feature full 3D, third-person graphics. Romancing Saga (1992) was an open-ended RPG by Square that offered many choices and allowed players to complete quests in any order, with the decision of whether or not to participate in any particular quest affecting the outcome of the storyline.
Test Drive III (1990) was a racing game where the player did not have to drive on a preset course, but could go wherever they want, i.e. drive off the road and onto the grass, hills and farms. Hunter (1991) has been described as the first sandbox game to feature full 3D, third-person graphics. S.T.A.L.K.E.R.: Shadow of Chernobyl was developed by GSC Game World in 2009, followed by two other games, a prequel and a sequel. The free world style of the zone was divided into huge maps, like sectors, and the player can go from one sector to another, depending on required quests or just by choice.
Nintendo's Super Mario 64 (1996) was considered revolutionary for its 3D open-ended free-roaming worlds, which had rarely been seen in 3D games before, along with its analog stick controls and camera control. Other early 3D examples include the Legend of Zelda games Ocarina of Time (1998) and Majora's Mask (2000), the DMA Design (Rockstar North) game Body Harvest (1998), the Angel Studios (Rockstar San Diego) games Midtown Madness (1999) and Midnight Club: Street Racing (2000), and the Reflections Interactive (Ubisoft Reflections) game Driver (1999). Sega's ambitious adventure game Shenmue (1999) was a major step forward for 3D open-world gameplay, and considered the originator of the "open city" subgenre, touted as a "FREE" ("Full Reactive Eyes Entertainment") game offering an unparalleled level of player freedom, giving them full reign to explore an expansive sandbox city with its own day-night cycles, changing weather, and fully voiced non-player characters going about their daily routines. The game's large interactive environments, wealth of options, level of detail and the scope of its urban sandbox exploration has been compared to later sandbox games like Grand Theft Auto III and its sequels, Sega's own Yakuza series, Fallout 3, and Deadly Premonition.
However, the series that had the greatest cultural impact was the Grand Theft Auto series. With over 14 million sales, some critics treat the release of Grand Theft Auto III in 2001 as a revolutionary event in the history of video games, much like the release of Doom nearly a decade earlier. Other critics, however, likened Grand Theft Auto III to The Legend of Zelda and Metroid, as well as Shenmue, and noted how GTA III had combined elements from previous games and fused them together into a new immersive experience. For instance, radio stations had been implemented earlier in games such as Sega's Out Run (1986) and Maxis' SimCopter (1996), open-ended missions based on operating a taxi cab in a sandbox environment were the basis for Sega's Crazy Taxi (1999), the ability to beat or kill non-player characters date back to titles such as Portopia (1983), Hydlide II (1985) Final Fantasy Adventure (1991), and various light gun shooters, and the way in which players run over pedestrians and get chased by police has been compared to Pac-Man (1980). After the release of Grand Theft Auto III, many games which employed a 3D open world were labeled, often disparagingly, as Grand Theft Auto clones, much as how many early first-person shooters were called "Doom clones".
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