On 07/11/2015 10:36, Andrew Errington wrote:
Hi all,
Here is a link to a random point on a light rail system:
http://osm.org/go/546Jvddtd--?m=
Soon after it opened I travelled on it from end to end, collecting gps
data and photos of all the station signs. There are two railway
lines, one in each direction, and I mapped them both carefully.
Recently I discovered that someone had helpfully deleted one of the
lines and tagged the other with tracks=2. I really don't think this
is acceptable.
I found the changeset and asked the user who did it why they destroyed
my work. They replied:
"The OSM wiki implies that a single way with tracks=2 is the preferred
way of showing rail lines with two tracks. This was the method used
most in S. Korea, I was attempting to create consistency."
This is not actually true (and I double-checked the wiki, just in
case). I pointed this out but the user did not acknowledge this was a
mistake, or offer an apology.
I'd definitely suggest that changeset discussions are the best place to
have this sort of conversation. That way, it's visible, so that other
people can be aware of the problem (and also discussions in public
tended to be conducted with more politeness). I'm sure that they
generally believed that they were doing the right thing, but didn't
think through the implications of what they were doing on data
consumers* and other mappers.
From looking at their edit history, which appears to be wide-ranging, I
suspect that they're a non-surveying mapper who may not actually have
been to all of the places that they've edited.
So, my question is, am I being unreasonable, or am I right to think
this is unacceptable? How can I guard against this?
There are a bunch of "who's been editing where" tools - one that's
especially worth mentioning is
http://wiki.openstreetmap.org/wiki/Quality_assurance#WhoDidIt which
looks for changes in an area and can provide an RSS feed. I also use
ITO's OSM Mapper http://wiki.openstreetmap.org/wiki/ITO_World#OSM_Mapper
. That works a few days in arrears, but is very useful at helping you
to visualise what has changed.
I have no
problem with people improving the map by improving the data, but I am
starting to see a lot of deletions, incorrect tagging, and generally
shoddy work appearing, especially in Korea where I have done a lot of
original work.
There might be a couple of issues here. One possibility is people using
"QA tools" to identify "problems" and "fixing" them. We've had a lot of
issues in GB with this - people changing the tagging on oneway roads in
carparks incorrectly when the _real_ problem was that not all of the
roads had been mapped is one example that springs to mind. Where a QA
tool identifies a problem, it should really be a prompt to carry out a
local survey rather than apply a "remote guess" of what might be wrong.
If I spot a problem like that I'd usually add to the changeset
discussion of the original mapper, or add an OSM note or a fixme, to try
and get it looked at properly. Sometimes not of this works and there
really are no local mappers, and the problem is bad enough that a remote
fix really is needed (perhaps a newbie has broken a major road by
mistake), but it's surely best that edits are done by people who either
actually are there, or at least have been there. Previous OSM tags +
imagery don't always give a full sense of what something actually is.
Related to this is people "correcting" tags that are "wrong". Often a
"wrong" tag is a really useful indicator that an inexperienced mapper
has been active, there are other things besides the "wrong" tag that
might been checking, and the QA report is a useful indicator of this.
Fixing the "wrong" tag removes the QA report but leaves the other data
that doesn't match the real world in OSM.
The other possibility to people causing problems using QA tools is
actually good news - lots of new mappers! People new to OSM will get
things wrong, whichever editor they're using, and any attempt to get
them to trudge through the mire that is the current "beginners' guide"
in the wiki will cause many to stop mapping before they've even
started.**. New mappers need help and understanding rather than "you've
done it wrong!". Often asking "what are you trying to map - how can I
help?" is a good way of getting to the root of the problem. I'd also
give new mappers a week or more to "find their feet" - I suspect that
the feeling of being watched would put some off too.
Do I have to set up some kind of watch on all of my
contributions and check them if someone edits them?
I did actually used to do this - I postprocess OSM data before using
mkgmap to create a Garmin map, and one of the things that that did was
to enable a list of "things edited since I last edited them" to be
produced. It's not something I've looked at of late though, since most
edits are perfectly valid and there are plenty of other ways of
identifying problems introduced by new (and old) mappers.
One other thing worth mentioning is whenever I've gone back to resurvey
something that has been "questionably edited" I've almost always missed
something that's either changed or that I missed the first time. I can
think of more than one example of someone changing "my" X to "their" Y,
and after I had gone and had a look I found that Y was actually correct now.
Cheers,
Andy (SomeoneElse)
* as a data consumer I don't really care what you're changing to what as
long as I know it's changing, no information is lost, and it doesn't
make it impossible to extract the information in the future.
** Compare http://wiki.openstreetmap.org/wiki/Beginners'_guide with
http://wiki.openstreetmap.org/w/index.php?title=Beginners%27_guide&oldid=1140764
to see the problem. Thankfully the person responsible for those changes
is no longer editing the wiki.
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