Just thinking off the cuff here:
Pick some starting points, and assign each a randomly drawn (hoped for) size. You can can maintain a separate size draw for planned continents and planned islands if you want.
Loop over the land elements, and where they are not yet at the planned size add one square. But the fun part is weighing the chance that each neighboring element will be the one. Some suggested thing that might factor in:
- Distance to the nearest "other" land. Further is better generates wide oceanic spaces. Nearer is better makes narrow channels. You have to decide if you're going to let bits merge as well.
- Distance from the seed. Nearer is better means compact land masses, farther is better means long strung out bits
- Number of existing land squares adjacent. Weighting in favor of many adjacent squares gives you smooth coast, preferring few gives you lots of inlets and peninsulas.
- Presence of "resources" squares nearby? Depends on the game rules, when you generate resource square, and if you want to make it easy.
- Will you allow bits to approach or join with the poles?
- ??? don't know what else
Continue until all land masses have reached the planned size or can't grow anymore for some reason.
Notice that diddling the parameter to these weighting factors allows you to tune the kind of world generated , which is a feature I liked about some of the Civs.
This way you'll need to do terrain generation on each bit separately.
