Maproulette challenges have become fairly popular recently, especially due to Jochen’s Area fixing project. But it seems this has gotten out of hand now and creates serious damage to the OpenStreetMap project.
In general this kind of tool is prone to inviting mechanical work. But with the recent Island and Shoreline Alignment challenge this really gets over the top. I first saw this when various edits turned up in remote areas of the world by various mappers in very high frequency editing islands in changing locations far apart within minutes, often without factual basis and often factually incorrect.
This challenge does everything wrong that can be done wrong with a fixing effort:
- there are no useful instructions to the mapper what to do and what problems to consider. It only says: ‘‘Align the highlighted island to match imagery’’.
- there is no documentation who created this task and how the allegedly misaligned islands are detected.
- and most importantly: the task covers areas where the global images routinely available offer no basis for improving the existing data.
Task: Align the highlighted island to match imagery (link)
Especially the last point is a big practical issue now since the edits made through this challenge misalign and worsen a lot of data in OSM. I commented on two most obvious cases where Bing offers no image at all but mappers none the less blindly followed the task to Align the highlighted island to match none-existing imagery with obvious results. But even in areas where Bing offers low resolution images these hardly ever allow improving existing data. These images in Bing are mostly from >15 years old L1G Landsat 7 images which have positional errors of sometimes more than 100m and rarely allow substantially improving existing mapping. In most cases attempts to do so made within the challenge worsen data which has often been mapped from either better data or with better alignment of the images.
With edits like this the island in question is not necessarily less accurate than before - the mapping before was done based on - if at all - only slightly better aligned images. But it is no improvement since it is likely not more accurate than before in absolute terms and is definitely less accurate relative to the surrounding features.
Yes, these images show a lot of potential to improve mapping here
The least that needs to be done here is
- stop the challenge as it is now
- limit it to areas where high resolution images are available in common sources
- create clear instructions for the mapper advising them to properly check image alignment and find the best quality sources in the area and check if existing mapping might already be of better quality based on other sources. This is not possible to do within a few minutes if you pick random locations all around the world of course.
Of course not all edits made within these challenges even in areas where Bing is poor are bad, there are also some experienced mappers participating here who know how to properly assess and select images.
If whoever created this challenge seriously wants to improve mapping in remote areas the most basic, most productive and most obvious way would be to provide better quality images.
And in general i think we need to put a review regime on organized mapping efforts like maproulette challenges requiring at least basic documentation of the process used to generate the task and ensuring there are proper instructions for the mappers and no nonsense tasks on a larger scale. A lot of thoughtful tasks have been offered in maproulette in the past but apparently this is not something that can be relied upon to be ensured without a QA process for the QA process…