Randomized boundaries, terrain of your choice:
A mini-tutorial for Paint.NET
Because Korash makes me do these things... and because there are like three tutorials on this entire gigantic forum that are tailor-made for PDN.
I got this idea while playing a number-puzzle game, of all things, called Logic Squares. All you really need to know is that it's similar to sudoku, in that when you've completed one you have a grid with numbers in it. I got the idea to assign a color to each number in one of the sets once I'd finished, and after a little noodling I liked what I got. So now I get to grace/inflict upon you the technique.
When I make maps, I nearly always use the method RobA and others have taught, where you render some clouds and let them determine your landmasses, elevations, bodies of water, and so forth. They look GREAT - but sometimes, I already have an idea of where I'd like water and land to go. In that case, I'd like a little more control over their placement, even though I still want to let the program come up with nice random boundaries between the different areas. This technique allows for that quite nicely.
One last note: I'm sort of thinking through this tut as I go; having written as far as step 2, I've already come up with and incorporated suggestions for several other different ways you could use this method. So if I seem inconsistent in places it's because I'm trying to teach and go stream-of-consciousness at the same time.
Step 0 - Program Prep
If you've never played with Paint.NET before, aka PDN, it's essentially a souped-up version of MS Paint. Yeah, I know what you're thinking, but you're only partly right. Out of the box, it doesn't have much, but it is open-source and there are over a hundred user-generated "plugins" that, when downloaded and added to PDN, bring it right up alongside GIMP in terms of functionality. Since this is a mini-tut, you will only need the Crystallize plugin, and optionally the Transparency Adjust plugin, but if you plan to stick with PDN for cartography, I'd also recommend Engrave/Emboss and Gradient Mapping at the very least. There's also a clouds plugin that I like a little better than the Clouds function included in PDN. Make sure your plugins are compatible with the most recent release of PDN - 3.5.6 as of this writing.
Step 1 - Build a grid
Your background layer is a simple frame, and it doesn't even have to be exact. Pick your preferred method of drawing either straight lines or rectangles, and make some.
I've gone as far as a 9x9 grid, but for this tut I'm keeping it simple and going with 4x4. You could probably go simpler, maybe even down to 2x2 depending on your needs - say you just want to establish the boundary shapes between three regions on a political map, for instance. I'm doing mine atlas style at the moment.
Note what I said earlier - my grid is not made of perfect squares. I could generate a perfect grid with another plugin I have, but all I'm making here is a frame for where I want color blocks to go in my next step. It really is okay for the rectangles to be unevenly sized.
Step 2 - New layer, nice big paintbrush setting, color in the squares
You don't even *really* have to go to a new layer if you don't want. I've just found that trying to put the colors on the same layer leaves some odd artifacts once I distort everything - probably because I'm not trying to be precise. This is quick and dirty, because the grid you're coloring in will *absolutely* not look gridlike once you're done. There's just no point in trying for pretty and perfect on this step, but since I don't want little black spaces on my map either, I go to a clean layer.
Pick a color you like for water, and then three more for land. Again, depending on the purpose of your map, you could use as many or as few colors as you wanted. If you were zoomed in far enough - say a coastal city or something - you could just use a water and a land color and call it good.
Select your paintbrush tool, bump it up nice and wide so you're not scribbling forever, and fill in the grid. (I'm currently at 50 pixels wide.)
Options: when I first played around with this technique, I strictly mapped my number grid because I was curious to see how it worked. This meant only one instance of each color per row and per column. It was fun and I liked the result. You might want to play with a 5x5 grid using these numbers:
But then I realized that the greatest asset of this technique is that you could deliberately choose where you want your regions to be, which means you don't have to follow that rule. Say you want a nice big ocean in one corner, or you want a row of mountains somewhere, or you'd at least like to show some elevation changes by color. Maybe you're doing a political map and you already know one of your countries/provinces/districts is bigger than the other/s. Go ahead and put a color into squares that touch each other. No, it's okay. Really.
You could also choose to fill in some squares with more than one color, say if you want small peaks on your mountains or a small lake in your land region, as I'm demonstrating here (along with another color for deep ocean). Don't get carried away with detail at this stage - and definitely don't try to add any more shape than what I'm showing you here - it will all go away in later steps, and your efforts will be wasted.
Note the gaps I've left here, with grid showing through. Yes, I could fill everything in more carefully, but as it happens those gaps provide me with an artifact that I happen to like. I suppose if I stayed on just my background layer the black artifacts could be useful too - it's just been a matter of personal taste so far that has led me to avoid them.
A final option is to use two layers to make this step - one for water and one for land. For now I'm not going to bother, but it's definitely a good idea, once you start doing texture-y things, to keep them separate. And, I suppose if you wanted to be really picky you could separate each color out into its own layer, but by then you're getting complicated enough that you've kinda negated the point of this tutorial.
Go ahead and hide, or even delete, your grid layer. If you plan to come back and do more experimenting with color placement, keep it around, but otherwise you are pretty much done with it.
Step 3 - Crystallize!
In PDN, this plugin is under the Effects menu > Distort > Crystallize. Its default setting is 8, which isn't a lot of deformation at all, in the grand scheme of things. Run your slider up around 50 and you'll see what I mean.
Play with the settings until you get something you like; I'm often surprised by the difference in results just going from 50 to 49, for example. I personally don't like to go higher than 65 or so, and only once have I gone as high as 80 - after that the "crystals" get so big that your color layout no longer fits your canvas, and you start losing large areas of your picture.
If you have a size you like, don't forget to try reseeding a couple of times to see what you get.
To be continued...