procedural generation - Generating tile map

I am programming a tile based game and I have some basic tiles (grass, dirt, etc..), but I can't figure out how to make good random map generation, because when I do some really random selection, if the tile should be grass/dirt, I get this:

I understand why this is happening, but what I want is to create some random continuous areas of grass or dirt. Something that would make more sense, like this:

Answer

What you could do is randomly generate a Voronoi map like this:

1. Picking random center points (see the black dots) and randomly decide if they are grass or dirt.


2. Then for over all tiles, check if it's closest to a center point of dirt or a grass.


3. Done!

If what you did previously is "flip a coin" for each tile (noise), generating a Voronoi diagram will provide a much better result.

You could improve on this by dividing the center points into islands with an algorithm that:

1. Picks a small group of centers points and designates them as leaders.


2. Iteratively adds a random adjacent undecided center point each turn.



3. Done!