## Monday, November 7, 2016

### An Excursion: Lots of Faults

After my previous posting about creating mountain ranges based on fault lines, over on Reddit Bergasms wondered what a map would look like with lots of small faults.  That's an interesting question, so I took a small excursion to try it out.

Bergasm asked about small faults, meaning ones that start and end on the map.  In my previous posting, I assumed that the faults stretched all the way across the map.  In my next posting I'll talk in detail about how to terminate faults on the map, but for the moment you'll just have to assume that can be done.

To start off with, I generated a bunch of faults that were about 15% of the map size and randomly placed them on the map.  I turned off perturbation, reduced the spread, and didn't generate any mountains so the faults would be a little more obvious:
You can see a scattering of pill-shaped faults.  This is 10 faults.
The isolated faults are a little jarring, but you can see in the lower right where faults are overlapping that the terrain is starting to look a little interesting.  Here's a map with 25 faults:
This is making some interesting shapes.  We can turn on perturbation to break up the regular shapes of the faults:

I think that makes a pretty interesting base terrain, at least as interesting as what we get from a noise function.  (It may be somewhat less "realistic", but that might be a feature for fantasy maps.)  I've seen some discussion of terrain generation using fault lines, but those algorithms typically use thousands of fault lines to generate a more jagged landscape.

Mountains don't work as well with these short faults.  If every fault generates mountains the map is nothing but mountains.
So we have to reduce the occurrence rate of mountains rather drastically.  But even so the mountains don't look very good because they are so short that they look like blobs rather than ranges:
There's also the problem that mountains stacked on top of mountains (as will often happen with lots of overlapping faults) quickly get unrealistic.  The central mountains here are 2X the height of "regular" mountains:

Overall I think I prefer the look of a map with a couple of longer faults:
But using many small faults to generate a base terrain as an alternate to a noise base seems promising.