I will be (mis-)using this issue to occasionally write about the current state of the effort to fix the (multi)polygons in OSM.

After a lot of preparation over the last half year or so (and frequent non-activity in between when I was busy doing other things), the real kickoff for this project was on February 14, 2017, when I posted the first challenges on Maproulette and made them public. Those challenges contained about 6500 self-intersecting building ways around the world split up into seven continent-sized areas. The community answered the call and got to work. Eleven days later, all of them were fixed.

While this was going on I worked on getting more challenges out the door. Next were about 1600 small landuse polygons from a single way with self-intersection I posted on February 21. They were all fixed in five days. I am amazed on how well and quickly the community responded, but there is muc more to do and not all taks will be so simple to fix. I deliberatly started with the easy tasks to get things going and give me and everybody else a chance to learn how this can work, before we start working on the bigger problems.

You can see the result of the effort in the massive drop in this graph (source):

That place were the number of errors was going up (February 23) was a massive import of broken data that got reverted a few days later. This shows another reason why it is good to fix those old problems: If the number of errors is much lower, anomalies such as broken imports will be seen more easily and we can fix them quickly.

On February 21 I also started another challenge: 1300 open rings from all around the world. As I write this, more than half of them have been fixed already. As these problems are (on average) much harder to fix, a slower pace then with the self-intersections was to be expected. But you can still the results of the effort in the graph (source):

I also started another challenge, to fix wrong roles on multipolygon relations. It is not doing as well as the others are, but it only has been going for a week now. And it has a lower priority, because those errors don't show up on the map directly. So it is good, mappers are working on the other tasks first. Ideally I'd still want the community to go through all those cases, because they show where the data is bad and problems often come in clusters. One error showing up in the challenge often means there are more around.

You can find all challenges and more information about how to help fix things here.