Lunaran.com Matthew Breit Level Designer | Texture Artist
This explains the concept of balance in a map layout by analyzing player behavior and movement in greatly simplified examples, and touches for a moment on the role of items therein. This article has stood the test of time much better than the other sections I wrote, and its only real flaw is that it doesn't carry the concepts far enough.
Jan 30, 1999
A single room, 256x256x128, has perfect balance. No part of the map will see more action than another. Fighting is the same across the Z axis, and the fragging can be done anywhere in the room with equal ease. Now, say we add another room right on top of it, with the same array of DM starts, and we cut a hole in the floor (picture). Balance is affected. Since there is no way to go from the bottom room to the top, but doing the opposite is as easy as falling in a hole, much more fragging will occur in the bottom room than does in the top room. This illustrates the fundamental balance-upsetter: gravity.
Take, for example, Q2DM8, the WareHouse, one of the point-release DM levels from ID. Balance, if it weren't for gravity, is about equal. There are about the same number of stairs between levels, so balance is fine there. But ... gravity. Players will commonly drop a good 256 units in pursuit of a frag (or escape of a pursuer), so you should consider a strong downward shift of balance wherever there is a chance to fall from one area to another, be it off of a catwalk onto the floor, down a pipe from one room to another, or from one level to another. A map with no areas of drop won't have to take this into account, like our small one-room map above.
Another universal balance-tipper to consider is the center of your map. Consider another map, nine identical rooms laid three by three, all connected to horizontal or vertical neighbors but not diagonal ones. If you set a bot to run around the map randomly from one room to a random one, choosing random paths, eventually, the average would show that he entered the corner rooms the least, the center room the most, and the four other rooms evenly. This has to do with the total number of paths from one place to another, with the most paths going through the center room. It works like this: each corner room has two neighboring rooms. Each side room has three neighbors, and the center room has the most, four neighbors (picture).
Consider Q2DM8 again. That room in the center with the rocket launcher, grenade launcher and stacks of crates is always seeing action. That room is in the center of the map, on the lowest floor. That and the two weapons and the two +25 medkits sway balance heavily towards that room. Back to our example. If we ripped out the center room, leaving only eight rooms in a ring, balance would be equaled again. The only paths you could take would be a clockwise ring or a counterclockwise ring. Each room has two neighbors (picture), so balance is equal.
The more complex and varied the floor plan of a DM map becomes, the harder it is to regulate its balance. Consider another example: four rooms of the same size, two by two, each connected to its two neighbors by a hall (but not to its diagonal neighbor). Balance between the four rooms is equal here, too. Each room has two neighbors. Say we choose one room, and lower the ceilings in the hallways leading to that room to 32 units from the floor. To reach that room, a player would have to crouch, slowing him considerably. That room would not see any action. Alternately, the room diagonal to that room would see the most action. It has two neighbors that are easy to get to. The two odd rooms have one neighbor easy to get to and one hard to get to, and the first room has two neighbors that are hard to reach. Say we lowered the ceilings on two opposite halls, isolating the rooms into pairs. Balance would be equal again, because each room would have one easy-to-reach neighbor and one hard-to-reach neighbor (but flow from one pair to the other would be obstructed (see below)).
Stairs and ramps can be seen as an equal-opportunity level connector (by levels, I don't mean maps. I mean stories, floors, that kind of level). It is just as easy to go up them as it is down them. So they don't affect Z balance. But, if the only way to go from one level to another is by way of one stairwell in the corner of the map, that area will be choked with people trying to use that one stairwell, and balance will be tipped heavily in the direction of that stairwell. It is a very effective bottleneck. One or two more stairwells generally alleviate the problem by adding more capacity and spreading it out in different points across the map, but a stairwell always draws attention no matter how many other stairwells there are.
Lifts are useful for upward balance shifting. As most of us know, the platform entity is incredibly annoying if you need to get down, but incredibly useful if you need to get up. The platform waits at the bottom, and when it detects someone on it, it goes up to the top of its path, waits for you to get off, and then goes back down again. This is all well and good if you need to go up, but it makes getting down difficult. Say I'm at the top of the lift shaft and need to get to the bottom. There's no way to trigger the lift to come up to get me, and even if I could do that, it wouldn't go back down until I got off. So, the only thing I can do is to drop down the lift shaft. *WHAM*, I lose a good 20 points of health, and what do you know? The lift detects me standing on it, and, being the nice lift it is, brings me back up to the top of the shaft again. A platform, therefore, isn't useful for going down, so it shifts balance upward. (The same XY bottleneck imbalance of stairwells applies to lifts). This is useful for countering the downward balance shift caused by falling. You should not put a lift everywhere that the player could fall to counter the gravity imbalance, because it could affect the flow of the map negatively (and platforms shooting up and down all over looks stupid and causes lag).