[HOT] Validating and imagery offset

Kretzer kretzer at gmx.net
Mon Oct 24 15:51:41 UTC 2016

Well, as I said, in most of the tiles I checked, the mapping was surprisingly good. I only did a little cleanup in some tiles, and reminded one or two mappers of the squaring.
But in my example there were cleanly mapped buidlings aligned to the provided custom imagery, and a well mapped road aligned to the Bing image which was quite offset. So I was wondering if it's the right thing to do to move the road as all the other features are aligned to the custom image.
Also most of the other newly mapped structures in the task would be aligned to the custom imagery. So I guess it's better to keep those? 
But in the end everything should be in the "right" place, shouldn't it? 


Gesendet: Montag, 24. Oktober 2016 um 16:38 Uhr
Von: "john whelan" <jwhelan0112 at gmail.com>
An: Kretzer <kretzer at gmx.net>
Cc: "HOT Openstreetmap" <hot at openstreetmap.org>
Betreff: Re: [HOT] Validating and imagery offset

This is my personal view after doing more than a fair amount of validation.
If you square the buildings you are making an approximation on what the original mapper mapped.  It doesn't look as pretty to leave it as it was but that is what I would do.  If mappers used the JOSM building tool to start with there wouldn't be the problem.  Garbage in garbage out I think is the technical computing term.  Politically you aren't supposed to delete the mapper's work realistically it can be faster to delete and remap using the JOSB building_tool plugin.  If you have the mappers for three hours I can get more buildings mapped with the tool than they can do in iD and its a lot more accurate, that includes the overhead for installing and configuring JOSM.
If the buildings are way out compared to Bing then you could select one displaced building and note the name.  Now search for all the buildings, within that search for the mapper.  Hopefully all their buildings will be displaced the same amount, move one building to alignment and the others will fall into place.  Again realistically if a building is six feet or a couple of meters out its findable so I don't even bother moving them these days.
Why even bother validating you may ask, well its the 10,000+ unlabeled ways in Africa, the 2,000+ highway=living_street in Nigeria the groups of buildings that should be tagged landuse=residential but are tagged building=house, the crossing highways, the highways that almost meet, the highway=motorway between two villages 200 meters apart these are the ones I try to catch.
Try to provide feedback, "added 97 buildings" if it nudges the mapper to do it right next time you've saved some poor validator a lot of work correcting but don't bother if it was mapped more than a month earlier.
I know I'm cynical.
Cheerio John
On 24 October 2016 at 08:03, Kretzer <kretzer at gmx.net[mailto:kretzer at gmx.net]> wrote:Hi,
as there seemed to be a need for validating the last Haiti projects, I did some tiles, though I am not very comfortable with validating - considering myself halfway experienced at best.

I found several tiles that were very neatly mapped, all the buidlings squared, although they were all done by new mappers ... probably that was a mapathon or something with good instructions and supervisison.

But I don't really know what do do when I hit structures that are mapped to different imagery whith quite a lot of offset, like here: http://tasks.hotosm.org/project/2229#task/188[http://tasks.hotosm.org/project/2229#task/188]
Should I clean this up while validating the "buildings only" project? How would I do this, align everything to Bing? (I remmeber having read that this is considered the most accurate). But then I would have to move around a lot of polygons, as all the new buildings are mapped to the custom imagery.
Or would you move the road to fit in with the majority of existing structures?

Thanks for your advice!

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