View Full Version : GIMP Mini-Tute: Making a Coast Outline, Island by Island

12-08-2009, 07:37 PM
This tutorial is simple and utilises the awesome tutorial by RobA.

Thread Link below
Making not so Random Coastlines in GIMP (http://www.cartographersguild.com/showthread.php?t=875)

**Don't forget, if you appreciate this thread, give the thread it's own little-rep-whack and try give it a few stars...**

This tutorial is to get around an issue I noticed when using RobA's tutorial to do multiple landmasses of very drastically different size. I noticed that smaller islands tended to get very "bland" coasts, while the big continents got nice jags and inlets. So I have tinkered to figure out how to get those big maps with nice detailed small islands and nice big islands. Using this method should allow you to do it without pulling your hair out.

So, onto the mini-tutorial.

Step 1
Begin using RobA's Random Coastline Map. Build the island, and stop once you have the "black jaggy island on black background". (Step 7 in RobA's Tutorial). Call the end result something like Island 1.

Step 2

Create a new transparent layer. Call it something like "Island 2" and set it to about 50% opacity (so you can see Island 1 poking through).
Fill it with black. Draw your chosen shape for your island in white.
Using the rectangle select select around the island.
Gaussian blur that shape by 50+ px. A lot of my A4 (300ppi) have 100px Guassian blur or higher.
Without removing the selection, create a new transparent layer (called Island 2 Noise). Move it below your blurred island shape and fill the selection with Render>Cloud>Solid Noise (Detail 15, X = 16, Y = 16). This should create a small noisy cloud with lots of detail in the selection area only.
Set the layer mode of Island 2 to Overlay.
Adjust the Colour>Threshold level until you're happy with the shape.
Merge Island 2 Noise & Island 2.
Set the layer mode of Merged Island 2 to Screen. Opacity should be returned to 100%.

You should now have a map with BOTH of your islands in a nice white shape against the black background. You can go in and edit either island by painting white or black onto the correct layer until you're happy with the results.

Repeat Step 2 until you have all the islands you need

Step 3: Complete RobA's Tutorial

Hopefully this will help people. I know it seems kinda simple and short, but it drove me nuts for a while until I had the chance to really tinker and play.

01-12-2010, 11:59 AM
Just finished my first try on Rob's tutorial and kinda wished I'd seen this earlier. I've noted this step down for my future endeavours =)

Thanks, and have a little rep.

01-12-2010, 07:05 PM
Glad to be of help Morrinn

01-12-2010, 07:10 PM
Hey you should post up a few demo islands created with the tut for those lazy cartotypes like me who would not otherwise try it. :D

01-13-2010, 12:01 AM
RedRobes> The smaller islands in this map (http://www.cartographersguild.com/showthread.php?t=8240) were done using this... but I will add demo ones below, they are easy to knock up.

01-13-2010, 12:32 AM
Image #1: Bare Island shapes. The kind you need for RobA's Tutorial. (150px Blur, Add noise layer, threshold, merge)
Image #2: Just going on with RobA's Method (to show you what happens)

Image #3: working on each a couple of the islands...

It's a fairly rushed job on the island shapes, but you get the idea. You can get some far better precision on each island (and insert archipeligos) without too must stress, especially when there are other large continents around.

You may also be able to get away with using a tiled noise pattern for large island to get that kind of "fine noise" to the coastline. But that is a later experiment.

Jason Wire
08-04-2012, 07:42 PM
Hey there,

Great tutorial, first couple of islands I did turned out great. Quick question... Now, whenever I do an island and get to the thresholding stage, something goes wrong. Rather than giving me a fractal-ish island shape, it gives me the exact shape that the gaussian blur took and simply expands and contracts that, filled with fully visible rendered clouds. Any advice?