Coastline flooding

Posted by Sil on 4 March 2015 in Dutch (Nederlands).

I’m new here, so it shouldn’t come as a surprise that not long after I made some changes to the coastline the entire continent of Archanta is flooded. Now, I had done some reading up on coastlines beforehand and only added a bunch of nodes.

After the flooding, I used to check if something had gone wrong, but thilo’s broken-coastline-node thing only highlighted a node on someone else’s coastline (in the east of AR045). IIRC there was an end node and a starting node which weren’t positioned right on top of each other. I put them together and merged the two lines.

Thing is, I don’t know what happens when the 2000 node limit is exceeded and now I’m kinda afraid merging the nodes may even have complicated the flooding.

I don’t know wether I am at fault here or what is causing the flooding, but if I am I want to apologize and hopefully someone more experienced is able to solve the problem.

Comment from Luciano on 4 March 2015 at 22:39

I think making some “floods” is part of the learning process. I’ve been doing a lot of work on coastlines, and have created a wiki entry about it too:

You can “split” a coastline way that is exceeding the 2000 node limit easily with a simple “p” command (“Tools>Split Way”) in JOSM (I don’t know about Potlatch or iD) and if you do only that, it won’t destroy the coastal integrity.

The biggest cause of flooding, in my experience, is not people manipulating their country’s main coastline. Instead, it is mostly caused by people using the natural=coastline tag incorrectly on “inland” elements that should be tagged as water or waterway or something like that, or when building harbors and then trying to “add” them to the coastline afterward.

One suggestion I have for mappers is when you want to build some complex coastal feature (river estuaries or harbors), don’t draw ways and try to then “cut” the coastline and add your newly drawn ways to the coastline. Instead, draw your features using temporary lines, and “drag” the coastline way into place, without ever breaking it, and delete your temporary lines when you’re finished.

If you ever exceed the 2000 way limit, just do a quick “Split Way” somewhere in the middle of your working coastline way (maybe even preferentially along a straight stretch of coast where you don’t have many features to make it easy to find and check).

Not sure if any of this helps. Anyway, don’t panic when there is a flood. A lot of people get angry about it, but it’s not hurting anything - it just looks weird in the render.

Happy Mapping

  • Luciano (Archanta Coastal Commissioner).

Comment from Rasmus Rasmusson on 6 April 2015 at 18:57

I’m usually working with iD (and sometimes Potlatch for larger scale things such as rivers and - since I learnt how to insert nodes in an existing line - also the coastline). iD gives you a warning when you’ve reached 2000 nodes and you simply can’t upload the change until you have found a way to reduce the number of nodes of the line - e.g. by splitting it. With Potlatch I haven’t encountered the problem yet.

Login to leave a comment