Everything's Gone Zombies: The Maps of Left4Dead

In Half Life 2 and other adventure mods, creating a map is usually based around the scripts and reactions for that one player. In Team Fortress 2 and Counter Strike, the maps are created to be balanced, and for the many players with in.

In the Left4Dead series, map creating gets a bit more complicated (no doubt resulting in the separate toolsets).
On one hand, the campaigns do have major 'events', such as those that trigger 'gauntlets' or the rescue attempts. On the other, the maps have to be balanced and prepared for the spawning of the enemy team in versus, as well as the generic zombie fodder.


In practice, Left4Dead maps are actually quite dynamic. It is a very rare event that you'll be given the same experience for a map. This is handled in a variety of ways, the main way being the AI Director. The AI Director provides control of the zombie spawns throughout the level, and this is based on the difficulty level and the measured 'emotion' that the players are experiencing, based on a variety of factors including how much damage individuals have taken. The AI Director also controls the spawning and placement of items and weapons, which depend on and alter the player's success.

In Left4Dead2, this AI Director gets another level of control: parts of the actual map.
In Left4Dead2 the map can change depending on how well the players have been, and can even be used to create near mazes. This is most vibrantly seen in the Cemetery portion of the The Parish campaign.

When it comes to mapping for Left4Dead, you have to be aware of both where the players are going and where the zombies will spawn, in the event of a random mob or a Boomer mob. You also  have to be aware of how the Special Infected's attacks interact with the environment. For example, in the official port of Mercy Hospital, a lip was added around the roof. If the mappers had not done this, the Survivor's life span would hinge mainly on the Chargers' successful attacks.
Though these maps do not actually use the exact same Hammer tool that we are using, I thought it would be interesting to note the different ways a game's scripting, AI and mapping come together.

Gabe Newell (2008). Edge Magazine Retrieved from

http://www.next-gen.biz/blogs/gabe-newell-writes-edge

Mike Booth (2009). Valve Software Retrieved from

http://www.valvesoftware.com/publications/2009/ai_systems_of_l4d_mike_booth.pdf

Alex J. Champandard (2009) Ai Game Dev Retrieved from

http://aigamedev.com/open/discussion/procedural-level-geometry/