[HOT] Broken (multi)polygon cleanup

john whelan jwhelan0112 at gmail.com
Thu Mar 16 21:23:47 UTC 2017

This is similar to my pulling in Africa a country at a time and using JOSM
to check for errors.

What I have noticed is one mapper will misstag then others will follow.  So
sanitising the area or checking it for errors before the new HOT mappers
start would probably improve the overall data quality as they tend to
follow what is already mapped.

Untagged ways by one mapper tend to cluster.  I've seen a 100 buildings in
one small area by the same mapper left as area=yes.  That's quick and easy
to fix.

Recently I came across 42 highways left untagged by the same mapper in the
same area.  The mapper had more than 2,000 edits so wasn't inexperienced.

Crossing highways often I'll see a town where the highway residentials are
laid out in a grid but the junctions aren't nodes.

Another nice recent one was a batch of settlements that had been tagged
highway=unclassified rather than landuse=residential.  Searching for
highways above unclassified and crossing ways picked those out quite

These types of errors are handled more quickly directly in JOSM than
involving maproulette.

Even the some other errors can be loaded up in the JOSM  to-do plugin.

I've been cleaning up in Nigeria for a while now.  Making repeated passes
over the same areas over time.  I'm seeing fewer errors so my suspicion is
the improved learnOSM, tutorials and simplifying what we ask mappers to map
is paying off.  Validating new mappers work within 48 hours does pay off in
data quality terms.  Giving feedback more than two weeks later is usually a
waste of time based on my own experience and Martin's report but I don't
think we have the validators to do the validation within the magic 24/48

Broken multipolyons do take a level of expertise to resolve.  I usually
avoid them.  However new mappers will fearlessly tread ahead and it is to
be expected they will break some.

I don't think learnOSM goes into detail about them or about relationships.
Should they?  That's another question.

For some errors we need boots on the ground.  Especially when it comes to
urban areas with limited access highways such as dual carriageways​ and a
highway approaching them can you turn in either direction?

Often the most motivated people to fix the errors are the locals who will
be using the map.  Trouble is we first have to get something in place that
is useful to get them motivated.

So yes HOT maperthons do have a reputation of the blind leading the blind,
ie some are led by inexperienced mappers but we are putting effort into
reducing the number of errors.  The training group has put together a very
good detailed set of instructions on how best to run a maperthon and if you
can identify a problem area HOT will listen and try to address the issues.

Cheerio John

On 16 Mar 2017 3:49 pm, "Jochen Topf" <jochen at remote.org> wrote:

> Hi Blake,
> On Wed, Mar 15, 2017 at 05:29:04PM +0100, Blake Girardot HOT/OSM wrote:
> > Can you send me something that would help me see those 1600 examples
> > you found on OSM so I can see what might be going on and how to
> > improve things in HOT/MM workflow to reduce them?
> Those 1600 are some very specific errors I am currently looking at, but
> only have those on my local machine currently. But for the wider picture
> you can use the OSM Inspectors "area" view to see the scope of the problem.
> Just go to any place where HOT/MM was active. Here is an example:
> http://tools.geofabrik.de/osmi/?view=areas&lon=33.65927&
> lat=-2.07600&zoom=8
> My current workflow is as follows: I choose one particular well-defined
> problem and extract the data from OSM that shows this problem. Then I
> put the data into Maproulette and document the problem and how to fix
> it. Some problems are easier, some harder to fix. Mappers can choose
> what problems to work on based on their skill level. If somebody
> doesn't feel comfortable with one of the harder problems, there are
> simpler ones they can work on. I also have some more general
> descriptions for the experts who want to go exploring/fixing on their
> own. Once the challenges are done, I choose a new problem and start the
> process from the beginning.
> Here are the current challenges: http://area.jochentopf.com/fixing.html
> Usually I am splitting up larger challenges into regions, for instance
> by continent or country. I could also do this by HOT activation area or
> so if that makes sense for HOT mappers. Splitting up, often makes the
> problems easier to fix, because problems inside an area are often very
> similar, but different to problems in other areas due to mapping
> priorities and methods. For instance, some regions have lots of problems
> with buildings, others with landuse areas, etc. Concentrating on one
> very well-defined problem at a time makes all this work simpler.
> Jochen
> --
> Jochen Topf  jochen at remote.org  https://www.jochentopf.com/
> +49-351-31778688
> _______________________________________________
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