How to Make Swamp/Marsh/Bayou/Delta next to a coastline

[wisemoon]

Hey everyone. I am working on a regional map, and the area is a very swampy peninsula. Think of it as a cross between Florida and Louisana (USA). When I look at Google Maps, the coastline of Florida around the Everglades, and the coastline of Lousiana near New Orleans, look very shredded to me (for lack of better terms). See these images for what I'm talking about:
FloridaEvergladesCoastline.jpg NewOrleansLACoastline.jpg

I have created regional maps using Rob A's tutorial, and I've created an atlas-style map using Ascension's tutorial. I played around with Rob A's method of randomizing coastlines, which is mostly using blur, random noise filters, and Levels adjustment. It's a good method, and I was able to get something interesting, but it wasn't the same kind of shredded effect I am seeing on actual land maps in Google Maps.

I'm wondering if anyone else has any ideas on how to get this effect? It appears that on swampy coastlines, as opposed to rocky ones, there is a lot more creation of islands, sandbars, etc. so the land edges are not as clear as they would be with a rocky coastline.

Thanks in advance for any comments or suggestions. Also, as I keep working with the experiment I will post some images of what I've done.

--wisemoon

[Diamond]

Well, with the Mississippi delta at least, all (or most) of that shredding is due to the sheer humungous amount of water dumped into the Gulf by the river. The course of the river changes, sometimes quite radically, over the centuries, depositing sediment into different places, cutting new channels, etc. You also have to take into account the damage wreaked on the coastline in both places by storms. With that in mind, I don't know that there's any sure-fire way to 'get' that effect other than to just draw it that way. If you really get stuck, you could always take bits and pieces of real-world maps, merge them together, and trace the result.

[waldronate]

The big reason for the shredded appearance of the Mississippi delta is that it's not allowed to flood its floodplain or change its course as such rivers do nearly continuously without intervention. The delta is largely unconsolidated sediments that are constantly compacting down; without a fairly constant influx of sediment across the delta, it will slowly sink out of sight.

Another fun point about coastlines that are sediments pretty much flat out into the water is that they change very rapidly, even in human terms. Sandbars rise and fall with the tide and upstream flow rates. A detailed map that you make this month may not be suited for navigation next week, and probably not next year.

Try applying the swirl and/or displace filter to the coastal areas generated by http://www.cartographersguild.com/tu...oastlines.html and also try easing the coastal constraints to get more offshore parts.

[Diamond]

^ His points are better.

[Naima]

I obtained some similar to "swampy" areas in my map while making tests and works , with wilbur .

You can try :
1 have a large flat area you want "boyouized" 1-10 pixel high
2 add a small filter like noise % 10
3 add magnitude noise 50 then fill mount 0.1
4 Erose the area in a selection with a feather of 2 - 3 with precipitation erosion 0.25 delta and passes 2
then you should have already a very dotted broken area
5 apply blur filter 3x3 box filter or higher according to if u want smaller or larger small islands .

This is what did the trick for me , but I actually didn't need those kind of lands so I sinked and evenized those areas with height clip 0.1-10000

[wisemoon]

<snip>

Try applying the swirl and/or displace filter to the coastal areas generated by http://www.cartographersguild.com/tu...oastlines.html and also try easing the coastal constraints to get more offshore parts.

I appreciate that tip! I've worked with RobA's GIMP tutorial (In fact I did an updated/revised version that you can find here) that was evidently based on this, but I haven't seen the original. I was trying to reverse engineer
RobA's techniques to work in Photoshop...turns out I was re-inventing the wheel! Plus the suggestion to use the swirl or displace filters is a good one, I'll have to try that.

--wisemoon