[HOT] Validating and imagery offset

john whelan jwhelan0112 at gmail.com
Mon Oct 24 14:38:46 UTC 2016

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

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> 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
> 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!
> K
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