Checkerboard islands
One final pastime for which I've used the random, hand-drawn checkerboards I've been writing about is generating lo-fi island maps.
To start, generate a large grid. This is one is about 100×100:
Starting at the upper right, color alternate regions blue, but only if they border the edge of the grid:
That makes ocean. Regions touching ocean are beach:
Regions touching beach are rocks:
Regions touching rocks are grass:
And regions touching grass are forest:
All other regions are mountains: