Left 4 Dead Design Theory

The are both single- and multiplayer coop games. In order to better understand the design behind L4D, you'll need to think diversely in both fields of Level Design.
*A good map is Fun to play on, and Fresh. The best maps can run on a 24/7 server without getting boring even after the second or third reload.
*A good map accommodates all player ranges of skill, and ability. If the player is failing or having a hard time progressing, neither should the map. Always make the map universal to all kinds of Players.
*A good map is designed, not simply constructed. If all you are doing is re-creating the surface appearance of another map, you're highly unlikely to create something worth playing in its own right.
*A good map is tested, tested, and tested some more. Then it is followed by more testing. Maps found in the L4D series are complex and third parties lack full technical documentation. L4D series maps rely heavily on AI (friendly and enemy bot navigation, bot interaction, and Director AI) that directly affect the player experience. It is practically impossible to release a good map that is not tested frequently.
== Gametypes ==
There are three game modes in L4D1 and four base game modes in L4D2. 
=== Coop ===
*Coop and Versus are deeply connected to each other in terms of design.
**One approach is to view Versus (roughly) as the foundation of Coop.
=== Versus ===
*Up to four human players will play as Infected.
*Human players need to be able to navigate areas that they expect to navigate.
*A map in Coop that is able to provide proper cover for spawns will translate well in Versus.
=== Survival ===
*Up to four human players as Survivors.
*Players must survive for as long as possible.
*Usually set in a single area with lots of supplies scattered around. (Typically areas that are panic events in normal campaigns.)
*Never ending waves of both Common Infected as well as Special Infected until the Survivors die.
=== Scavenge ===
*Similar to Survival and Versus. Up to eight humans can play this mode. (Four Survivors, four Infected.)
*Survivors must collect gas cans and fill up a generator under a time limit. (Similar to Dead Center and The Passing's finales.)
*Every gas can poured adds a little extra time on to the timer.
*The Infected team must try to stop the Survivors from getting gas cans. The team with the most gas cans poured will win.
=== Mutation ===
This isn't exactly a single game mode but, in a sense, an infinite number of game modes. Mutations are capable of modifying a base game mode by combining non-default cvars and utilizing VScripts. A mutation is allowed to use cvars usually marked as cheats. Mutation VScripts rely on director options, specialized and non-specialized hooks, and functions.
Maps can be designed specifically for a certain mutation or a mutation can be designed around an existing campaign or single map that has matured via feedback in base game modes.
== Design ==
Left 4 Dead takes place in a cinematic apocalyptic setting filled with zombies. That being said, L4D follows a pseudo-Counter-Strike: Source-type weapon and bot navigation system. The reliability of the navigation mesh holds the same weight of importance as the level design itself and the two categories are inseparable. The pacing of the game is directed by an AI called the AI Director. The AI Director collects data about player state in real-time, consequently determining enemy placement/state and item placement/type in a procedural manner. It is capable of delivering a dramatic experience all by itself while flexible enough to be able to follow parameters given by the map designer.
===Environment===
Your first goal before starting should be to think like a zombie, but without the idea that your goal is to kill the survivors. The game heavily relies more on the actual waves of zombies influence rather then the players. Because of this zombies can reach just about any height, if of course there is a way to climb up to it.
When thinking about the kind of environment you would like to design, consider the kind of situations the player might find themselves in. Because no one has really lived an actual zombie apocalypse, it's up to you to continually playtest through each of your areas to understand natural decisions any survivor may make. The waves of zombies are dynamically controlled in each section of your map, meaning any real area can be dangerous because of this.
Left 4 Dead excepts non-linearity because initially you are designing your map for two parties: The Survivors and the Infected.
===Aesthetics===
;Lighting
A large factor in the design for Left 4 Dead maps is the lighting. Lighting and environment cues are the main ways the level designer can guide the player around the map, as well as giving mood and texture to the map. The original Left 4 Dead maps use a lot of classic horror movie lighting techniques, and you will find that your map will look a lot more professional if you hold to these techniques as well.
These techniques include:
*Low-angle lighting - Light sources are placed close to the ground so that the shadows are cast upwards.
*Bright vs Dark - Players will naturally be atracted to light areas and deterrerd from dark areas, and the designer can use this to their advantage. 
*Stark contrasts - A very bright area surrounded by darkness is a good way of attracting total attention, and sometimes triggering tunnel vision, the high contrasts in light also give the area a more ominous feel.
;Prop placement
Remember that the game is based in a post-zombie-apocalyptic world, so the electricity would be out and there would not be many well-organized areas. A good rule of thumb is that if you can envision people working or living in the environment without a worry, you probably haven't made it derelict enough. Although, by the same token, overcrowding the area can be detrimental to focus and misleading or frustrating to the player.
Left 4 Dead uses a lot of different decals to bring the world to life, including graffiti decals and community notices. These assist with the players suspension of disbelief by providing more evidence that the world has gone crazy. If a wall looks suspiciously bare, a poster or graffiti spray can help it blend into the environment better.
The world Left 4 Dead takes place in is, or has been, undergoing panic and chaos among the residents that once lived in the cities and towns you venture through. A good thought to bear in mind is that most stores, city streets, and homes have been looted or set fire to. Along with this, military vehicles or police cruisers set through-out your maps help tell the story. Of course, it is entirely up to you based on whether or not the situation calls for such details.
== Construction ==
== See also ==
* Left 4 Dead Level Creation
* Left 4 Dead 2 Level Creation
* Left 4 Dictionary
* Optimization (level design)
* Dissection of Official L4D2 Campaigns
* What makes a good level?
== External links ==
*CGSociety Left 4 Dead 2 Feature Special - Interview with character designer Jeremy Bennett and environment designer Randy Lundeen
*Edge Magazine The Making Of: Left 4 Dead - Article, "Valve’s co-op take on undead horror redefined online play and scared us witless. Not bad for an apocalypse with just 30 zombies."
*Gamasutra Why Left 4 Dead Works - Design analysis by Paul Goodman, Adams Greenwood-Ericksen
*Left 4 Dead Nation - A website devoted to competitive L4D and maintained by the author of the popular competitive server plugin Confogl. This can be used as a resource on level design for Versus or any other competitive multiplayer game mode.
*Left 4 Dead Blog
**L4D Art Direction, Part 1: Filmic Effects - Randy Lundeen, Valve
**L4D Art Direction, Part 2: Stylized Darkness - Randy Lundeen, Valve
**Left 4 Dead 2's G4TV Interviews - Interview with Dario Casali about L4D2 level design
**12 Terms from the Left 4 Dictionary - Phil Co, Valve, lays out 12 terms from the Left 4 Dictionary
*Left 4 Dead Wiki 
**Left 4 Dead Commentary - Developer commentary transcripts
**Left 4 Dead 2 Commentary - Developer commentary transcripts
Category:Left 4 Dead
Category:Left 4 Dead 2
Category:Level Design
Category:Theory