Population density

Virtual worlds need to manage their population density. If a zone is deserted, playing there isn't any more interesting than a single-player game. But if there are too many people at the same spot, players get into each others way, and the loading of all the character's textures causes lag. So game companies need to manage how many people are allowed on a server, and take measures to distribute them well over the different zones.

World of Warcraft gets the distribution part right most of the time. One reason for that is that unlike many other games, WoW can largely be soloed. The other big reason is that the quest system strongly rewards you for moving and seeking out all the different corners of the world. The counter-example, of how not to do it, is Final Fantasy XI. In that game you can't solo, but need a group in a very narrow level range. And there aren't many quests, so most of the time you are just grinding mobs to level. As a result people tend to all gather in one zone for a specific level range. For example everybody from level 10 to 20 is in the Valkurm Dunes. There is another zone of identical level range, Buburimu Peninsula, but it is nearly deserted. You can't go there, because you can't find a group there. So everybody is standing on each other's feet in the dunes, and never sees another zone of that level. Boring through bad game design.

But even World of Warcraft isn't perfect. One major distribution problem is between Horde and Alliance. Yesterday I did a census on my main server, a 2 year old European realm, and found 800 Horde players and 1800 Alliance players logged on at 6 pm. Alliance traditionally has a higher percentage of casual players (apparently attracted by being able to play humans and sexy elves), and the recent pre-BC raiding slump seems to affect Alliance less than Horde. Blizzard is trying to fix that, by giving the Horde sexy elves, but we'll have to see to what extent that works. Meanwhile the difference in numbers makes for long Alliance PvP waiting queues, and for more lag in Ironforge than in Orgrimmar.

Distribution becomes a catastrophic problem when there are world events. Everybody who experienced the opening of the gates of Ahn'qiraij saw major lag, and probably even a couple of server crashes. In Star Wars Galaxies players unhappy with some changes to the game tried to stage a protest march, and the GMs had to forcefully disrupt that and teleport the participants to other planets, because the servers simply couldn't withstand a large gathering of characters.

It is predictable that World of Warcraft will have big player distribution problems when the Burning Crusade comes out. More than half of the players of WoW have at least one level 60 character, and they all will want to visit Outland. But there is only one portal to go there, and only one zone to level up from 60 to 62, Hellfire Peninsula for both Horde and Alliance. Thus it is likely that we will see half of the population of each server concentrated in one single zone. That could cause crashes, but at the very least it will result in lag. And with players outnumbering mobs in the zone, doing the same foozle hunting quest as everybody else will be a pain. Blizzard is working on a "dynamic" spawn system, but in the beta it wasn't working well.

As long as a game is growing, distributing players among the servers is manageable. You can split overpopulated servers, or offer free or paid character transfers. Somebody is always tempted to leave a crowded server and start fresh on a new server. The population density issue becomes far more difficult to handle if the number of players is shrinking, which happens sooner or later in every MMORPG. Especially the lower level areas of a game tend to become less and less populated with age, leading to problems in finding groups. Also the player economy suffers when the player numbers fall below a critical size.

I wonder how World of Warcraft will handle the expected strong fluctuations of player numbers in 2007. I'm sure that the Burning Crusade expansion coming out will cause many people to reactivate cancelled accounts, with player numbers shooting through the roof in January / February. But I don't think that this increase will be permanent, and I'd expect that peak to pass after a couple of months. Blizzard will open up new servers simultaneously with the expansion coming out, and reportedly increases server capacity by 25%, argueing that the land mass also increased by 25%, thus the population density would remain constant. Personally I think that the old continents will be relatively empty, the new continent relatively crowded, and once the wave of new blood elves and draenei has passed, low population density in lower level zones will become a real problem.