How can I ensure procedural levels in an RTS are fair?

In some cases, it might be possible to rely on the players themselves to build balanced asymmetrical maps by using tile manipulation mechanics.

At one end of the spectrum, you can allow the players to create the map, either partially or entirely, by selecting & place map tiles. There are a bunch of different ways this could be tweaked:

• players select from a common deck of tiles
• layers select from a personal deck of tiles
• tiles are selected via a drafting phase
• some tiles might be fixed in advance via scenario (i.e. always spawns a bridged river across the middle of the map)
• players purchase tiles from a central market with some resource
• players may or may not be allowed to keep a hand of tiles

At the other end of the tile manipulation spectrum is allowing the players to manipulate map tiles. In this solution, the game start with an initial map. The initial map could be symmetric or might be 'fair enough' by using any of the other answers.

Next, a map manipulation phase occurs in which the players may do some of the following:

• rotate a tile
• swap tiles (adjacent or otherwise)
• mirror a tile
• push a row or column of tiles (tile that would fall off the edge wraps around)

These manipulations could be executed one at time, in which case one player would have a chance to react to another players manipulations, or the player might queue of a list of changes which get executed. Also, you could allow players to manipulate the entire map, or restrict things to their starting areas.

A drawback of this approach is it the final result needs to be guarded against undesirable outcomes - i.e. manipulating an impassible mountain range such that part of the map becomes inaccessible. Possible solutions for this drawback are:

• checking potential moves & disallowing ones that lead to illegal outcomes
• allowing all moves, but undoing anything that is illegal
• building the tiles so that no moves are illegal
• designing other game mecahnics (i.e movement) such that no moves are illegal

Have your map generation algorithm generate symmetric levels by generating a level, mirror it, and place each player on one side. A four-player map can be created by mirroring it on both the x- and y- axis.

That way the map will be equally good (or bad) for all players. A side-effect which you need to be aware of is that it means that the players are aware of the positions of the other players and of the layout of the other parts of the map after exploring their own.

Another option is to generate a map without this symmetry trick, but then show the whole map to the players and have each player pick their starting location freely.

One approach is to use other factors to balance the map. You might be able to automate this by using some map analysis algorithms & providing extra starting resources to locations that are deemed disadvantaged. Alternatively, you can use the players themselves for this step. A current example of this is the use of reverse auction in reveal mode in Offworld Trading Company (OTC) for founding your initial claim (i.e. picking a starting base location):

As time ticks by, the starting debt for founding early goes down. This will eventually turn into starting money if it takes a long enough amount of time for the last 2 players to found. Once there is only one player left who hasn't founded their HQ, the values stop changing and that player no longer gains from waiting to found.

I don't recall if it was the 3 Moves Ahead or Game Design Round Table interview, but in one of them Soren Johnson (the developer) says this mechanic essentially changes the map problem from "can I find the best location first" into "how good is the 2nd best location on the map."

A benefit is this solution allows highly asymmetric maps. A disadvantage is that the entire map is revealed to all players, at least at the beginning. The OTC approach also reveals player base locations. Other mechanics like blind bidding, might avoid revealing base locations.