[OSM-talk] Identical Duplicate buildings

[Pierre Béland]

Hi Stephan
No simple response to such duplicate problems. And they are part of a bigger Quality problem. They can be related to the tools, the experience of particpants, the internet connection as said, training and orgnisation of mapping activities.  If there were systematic duplicates added, tools like Osmose would alert us.

Big Mapathons are «good labatories» to explore mapping practices and eventual problems since you have in these events an important number of newbies often mapping once and never coming back or not participating intensively. The Nepal earthquake response in 2015 was the first time that we had a huge number of newbies participating to mapathons for only one day. They represented nearly 70% of participants (see https://www.slideshare.net/pierzen/kll-workshop-2015-0809-openstreetmap-response-2015-nepal-earthquake).  Since then, we saw this participation increasing in mapathons and validators did struggle to analyse - correct the data. Gladly, we see that editor Tools evolve to better support the mappers and provide more validation.

Tasking manager activity statistics can be a good start to find dates / areas to look at. For example, Butembo around 2018-12-11. See discussion about that https://lists.openstreetmap.org/pipermail/hot/2018-December/014662.html
The Overpass script below concentrates on buildings only for 2018-12-11 for Butembo. This was just after an intense week of mapping with problems reported on the HOT discussion list. Interesting to download the osm data from Overpass download panel in JOSM and run the validator.  
JUST BE CAREFULL TO NOT UPLOAD THAT TO THE OSM DATABASE.
[out:xml][timeout:60][date:"2018-12-11T00:00:00Z"];way  ["building"]
  (0.081195804121638,29.247150421143,0.17509433195814,29.342937469482);
out meta; >; out meta;
 We dont see systematic duplicates. Other then duplicate buildings, we see that sometimes only one wall is duplicated, sometimes back and forth. Generally hard to spot such problems and the validator helps find them. Not only newbies make such mistakes, and like others I experimented intermittent internet problems while in Haiti. 

I think that there is a good chance that experienced contributors will realise the problem and correct rapidly. The many validator rules added to JOSM now help to spot these problems more rapidly and correct.

Solutions are two folds. The Tools can better validate and instruct mappers to correct them. The unsquarred buildings traced in iD are still a problem as the building tool is less intuitive then in JOSM.

Organization of mapping is also important. In mapathons, validators could use JOSM to regularly download the osm data for the area of the task the group works on and use the JOSM validator to detect problems.  This would be also the opportunity to interrupt the mapping session, use a projector to show  a session, show the problems observed via JOSM, go back to iD or JOSM editors to show how to map, detect / validate.

 
Pierre 
 

    Le vendredi 29 janvier 2021 05 h 49 min 01 s UTC−5, Stephan Knauss <osm at stephans-server.de> a écrit :  
 
 Hello Pierre,

On 28.01.2021 23:13, Pierre Béland wrote:
> good news that you can manage to fix this in the iD editor. Discussion 
> about quality did not focus on the Editor tools.

I am sorry, if the wording caused some misunderstanding. To make it 
explicitly clear:
I did NOT do any fixes in the iD editor. I corrected OSM data by 
removing the mentioned duplicate geometries. It did affect roads or nodes.

The common part was, that IMHO it was often iD and that that the same 
user did the upload of the exact same geometry/tagging a bit later.

This was leading me and, by reading this thread, others into thinking, 
that there is a possible work-flow in which users unintentionally upload 
duplicate objects.

I use osmose to detect such issues.

If you see massively higher numbers somewhere else it might be 
interesting to see what is the common part here.
There was the suspicion that a specific usage patter triggers this, like 
early closing of the editor. But then I would expect it to happen 
everywhere with a similar probability or it concentrates on specific 
users having this pattern. I did not observe this.

Maybe it is related to bad network connectivity? This might explain why 
it is more frequent in areas which have lower network quality.

One example. This node was duplicate:
https://www.openstreetmap.org/node/6506144132/history#map=19/13.74290/100.52013

In this case the editor identified itself as "OsmAnd+ 3.3.8".


Another example:
https://www.openstreetmap.org/node/7899874464/history
Editor in this case "iD 2.18.5"

You could find them using osmose. Some areas have more of them, than 
others. In total we are at roughly 6.900. See the graph for a 
visualization of the changes over time.

http://osmose.openstreetmap.fr/en/errors/?item=1230&class=1

http://osmose.openstreetmap.fr/en/errors/graph.png?item=1230&class=1

Unless you are looking at one of the top countries, the numbers are all 
in the lower two-digit range. I recommend manually checking and fixing 
them. Often you see this way other issues which needs fixing as well.

Stephan

  
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