How to create biomes

Question

I am creating an 2D XNA Tile Based Platformer. I have a tile engine and a world/terrain generator. However, I am trying to create biomes or areas, For example, Desert in one part of the world, ocean on the ends, City in the middle, forests scattered around etc. I can easily make it generate them, but My problem is defining the actual areas to be generated in.

Answer 1

Without any specific knowledge of your generation algorithm, I would suggest the following.

Assuming that your world is defined in a multi-dimensional array Tile[999,99]

1. Decide how many "biomes" you want and of what type
2. Define the size of each biome
3. Go through your world array, and pick a start point for each biome
4. Update the world array with each biome's tile data

For example:

Tile[,] World = new Tile[999,99];
Tile[,] Ocean = new Tile[50,10];
// assume we want the ocean to be top left of the world, flowing off the edge
for(int i = 0; i < 50; i++)
{
    for(int j = 0; j < 10; j++)
    {
        World[i,j] = Ocean[i,j];
    }
}

You could, as @Nathan suggested, use a distance from water to define which tile-set to use for each area. This could help keep your maps looking fresh and consistent, yet still be generated on-demand.

Answer 2

There is a great discussion of procedurally creating random biomes on a map in Polygonal Map Generation for Games by Amit Patel. His maps are arbitrary polygonal shapes, not tiles, but the same ideas should be applicable.

Briefly: generate elevation and lakes/rivers on your map using whatever method works for you, then define biomes in terms of elevation and moisture (distance to water). There is a nice table in the article that suggests different biomes for different combinations of elevation and moisture level.