Hello everyone. This is actually my first time posting here, but after all the work I did, I was hoping to spare someone the time and agony I went through. These instructions are specifically for Pixelmator on the Mac. I posted them on my personal blog at Creating Coastlines for Maps in Pixelmator | -rks, but I've copied a rough version of them here.

If there are details or information missing, please let me know. I pride myself on my tutorials (I used to write this kind of stuff for a living), but I find myself guilty of often missing things.

I hope it helps!

Section 1: The Pieces

  1. Drag and drop desired “background” image into Pixelmator and label this as “Land” for the sake of simplicity.
  2. I like to do parchment-style backgrounds as it makes the
  3. Click the box to the right of Land to deactivate the layer.
  4. Create a new layer by pressing the + button in the bottom right hand corner of the layers window. Name this layer “Coast.”

Section 2: The Coasts

  1. Click “Brush” icon in your tools window and use an Artistic brush to draw the islands/coastline.
  2. Play with different kinds of brushes, though I found the Artistic brushes very effective. Make sure to add a little scatter to them. The idea is that there are no clean edges. Jitter as you draw, you don’t want them too even.
  3. To access the different brush sets, click the Gear icon within the Brushes Window.
  4. I prefer to keep the Blending set to normal, but feel free to adjust it as you see fit. Dissolve tends to be a little too pixilated for me.
  5. Make sure you do it in short strokes. Not only is it easier on your computer, but if you make a mistake, you have to redo less.
  6. Use a large brush for “smoother” sections of the coast and then use a smaller diameter brush for the finer detail. Add some outcroppings and bays, depending of course on the landscape you want.
  7. Try not to leave any large gaps inland as it can throw off the next step. I recommend doing lakes and rivers by hand in a separate layer.

Section 3: The Selections

  1. Once you are happy with your coastlines, use the paint selection tool to select the area inside of the painted section.
  2. Switch the mode to “Add to Selection” (top left of the screen, two solid boxes on top of each other) and select any other section of any islands.
  3. Click on the “Erase” command and change the brush style to something large and solid.
  4. Go to Edit > Invert Selection and then erase everything around the coastlines, so you don’t have any stuff left over.
  5. Go to Edit > Invert Selection again and then erase what’s inside the landmasses.
  6. Now you should just have a large selection on an empty background image.
  7. Make sure you don’t have any “holes” in the landscape, otherwise you may have to go back and reselect them with the paint selection tool.
  8. Select both the Land and Coast layer.
  9. Right click the selection and choose “Add Mask”

Cleaning Up

Group both layers and name them (“On’onar League” “Athlon Sea Commonwealth” “Western Reaches,” etc) to make things easier to identify.