On 22/03/2016 13:10, Frank Villaro-Dixon wrote:
Hi everybody,
So, what do you think ?
I think it's a silly idea.
Identifying complex potentially problem areas is one thing - as you've
found, attempting to fix them automatically is quite another. In among
the "obvious" fixes will be many harder to find new problems that you
have introduced.
Technically, it was already run on the whole planet, and so far no
bugs were found.
That's not true. Many people complained and all your work was reverted.*
Now, I need your comments and/or your approval, critiques, etc.
Tell me what you think ;-)
Here's what I think you should do, when you detect a potential problem:
1) Firstly, before fixing anything, try and understand what the cause
was. Perhaps an inexperienced mapper has edited some existing data that
broke something that they didn't understand? You'll need to look at the
mappers who have contributed to the problem, their relative experience,
and what editors they are using (for example, an iD user may been not
have seen the complicated reationship between multipoloygons, and a JOSM
user may have stopped thinking about real-world data and thought _only_
in terms of multipolygons - both can cause errors).
2) If you can, go and actually survey the area. No, really, do actually
go there. That way you'll get a full 3d picture in your head of what's
there and how it relates to the aerial imagery. It also enables you to
recognise features from imagery better, so you can see what sort of
surface a path is, and (with water features) tell man-made ones from
natural rivers and streams (difficult from imagery, especially when made
by man 200 years ago). Maybe the area is inaccessible to everyone, in
which case anyone would have to work from imagery and other out of
copyright sources, but if it is accessible to local mappers then they
are the best people to fix any problem because they will be able to do a
proper survey.
3) You'll now have a picture of (a) what the original mapper had in mind
when they mapped it, (b) what subsequent mappers were trying to do and
(c) what you'd have mapped it as, if you had mapped it from scratch.
If these three all agree, and it was just a tagging error (for example
I've seen people add "natural=foo" instead of "name=foo" recently) then
it makes sense to "just correct the data". However, it's quite likely
that these three might disagree, and perhaps you need to explain to an
earlier mapper how multipolygons work, or to someone who has come along
and "corrected" data in the interim that what they've changed something
to is a valid OSM tag, but doesn't actually match what's on the ground
in this case.
The best way to try and communicate with a specific previous mapper is
via a changeset discussion comment. The advantages of doing it this way
are that the discussion is public, and the context is obvious, as it's
visible with the changeset. Other local mappers can also add comments
there too - perhaps someone else locally has more knowledge about a
particular water body. If that doesn't work, or you need to contact all
local mappers you can try adding an OSM note explaining the issue. This
might not get picked up immediately but notes sometimes do get fixed
many months after they were added. Another option is to try and contact
local users via a country's mailing list, forum or IRC channel. They
may know someone who is local, or know someone who knows someone (not
necessarily an OSMer) who may be able to answer questions.
Based on the above, I don't believe that it is possible to do the sort
of "water fixup" that you were trying to do entirely automatically.
http://wiki.openstreetmap.org/wiki/Automated_Edits_code_of_conduct has
sections that require you to "document and discuss your plans" for a
reason. To take a specific example, I noticed local edits made by you
in http://www.openstreetmap.org/changeset/37086092 that simply failed to
understand what the original mapper was trying to represent. I pointed
this out on the changeset discussion, and was frankly amazed when you
created a bot account to make more of exactly the same sort of error,
again. Maybe I'm the frog in
https://en.wikipedia.org/wiki/The_Scorpion_and_the_Frog :)
There may be many scenarios that you haven't considered when designed
what automatic changes you are trying to make. Other mappers will be
able to help you understand those when you discuss your plans with them.
Also, please don't think that "changing a tag to one that is valid
within OSM" means "making the data correct" - it doesn't. All it means
is that it is no longer possible to automatically find potentially
problematical areas needing survey, or find mappers who may need help to
map better. In an analogy, if someone has described a "horse" as a
"kow" correcting the spelling to "cow" does not make the description
correct.
Finally, please remember - OSM is about geography, not computer
science. Your account has made relatively few edits and few if any of
these seem to be based on actual survey. I would strongly suggest that
you take a little time out to actually do some real survey-based
mapping, and in addition spend a bit of time understanding the human
causes of the sorts of problems that you're aiming to detect, and
helping those people understand the resulting problems in the data.
Don't just say "you did X wrong" - explain to them politely how and
offer to help them get it right next time.
Best Regards,
Andy Townsend (SomeoneElse)
* as well as being an "ordinary mapper", I'm a member of the Data
Working Group and saw the discussions as these changes were made and
reverted.
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