[OSM-talk] Trace type

[Ed Avis]

Andy Allan <gravitystorm <at> gmail.com> writes:

>>By analogy, when adding a street to OSM, most editors do not just show a
>>blank textbox and expect the user to enter key=value pairs manually.

>You need more understanding of the history of how OSM grew - the
>editors did used to just throw up blank textboxes and everything
>worked fine. The usage came first, then consensus, then presets.

Hmm, you have a point.  But still, what worked back in the early days of
the project, when a small number of fervent OSMites wandered the desert
with GPS devices surviving on honey and locusts, is not necessarily the
best answer for a much bigger user base.  Certainly the project gets far
more contributions now than a few years back, and while there are several
factors that contribute to that (the aerial imagery, momentum, and so on),
I would suggest that one reason is we have user-friendly OSM editors which
provide clickable choices rather than expecting you to remember tags.

(I know that when I started mapping I didn't enter some POIs or information
because there wasn't a menu item for them in Merkaartor.  Mostly, I just
didn't think of adding them.)

Remember we are discussing meta-information about GPS traces rather than
the map itself.  And there are some important differences between map data
and GPS data.  If something is tagged vaguely or in a non-standard way on
the map, then it can always be cleaned up later.  amenity=hotel can be
changed to leisure=hotel; note="This is a pub" can be changed to amenity=pub.
But with a GPS trace that isn't clearly labelled, unless you can contact the
original uploader and get them to remember the details, the information is
lost.

Another person on this list mentioned that he didn't think of tagging
traces with the mode of transport used.  There's no prompt for it when you
upload a file, and so most people don't.  Similarly, I never thought until
now of adding the model of GPS I used, until by chance someone happened to
mention it on the mailing list.  And even now that I know I should add it,
it's far from obvious how to do so.  If there were a simple text box labelled
'GPS unit used' then I would have filled it out on every trace uploaded, and
so, I assume, would hundreds of others.

>Maybe this is the point you're missing - we already have conventions
>on tagging GPS traces. "car" outnumbers "motorcar" by orders of
>magnitude.

Let me explain what information I think is useful, and then it may become
clear why the current single textbox is inadequate.

When you view GPS traces in an editor to add or adjust ways, it's important
to see how they were made.  If you have a mixture of foot and vehicle tracks,
then at best you can add ways as footways, unless you have other information.
If you know that the tracks are all made by motor vehicles and nothing else,
then you can trace them and tag as roads.

What happens if I drive in a car then get out and walk?  If I tag the trace
as 'car', does that mean that the whole trace was made in a motor vehicle, or
just part of it?  Someone viewing it in an editor and looking for 'car' traces
might mistakenly trace my route and make it a road suitable for motor vehicles,
when in fact I was just following a footpath for that section of the trace.

Perhaps, you might suggest, all methods of transport used should be tagged.
So if the trace has 'car,foot' then it is a mixture of the two, but just 'car'
would mean exclusively in a vehicle.  That could work, but you have to be sure
that the person tagging their GPS trace did indeed follow this convention.
(Should they add a 'following_gps_trace_tagging_convention_version_1' tag
to their traces?)  But also, every editor would need to have a list of all
method of transport tags.  If I tag a route as 'car,pogo_stick' but then
someone loads it into JOSM, which doesn't know that pogo_stick is a method
of transport, then it would display as a motor vehicle GPS trace.

(Another fun wrinkle is that 'car' is a placename in some parts of the world,
but we just jumble place names, transport, and other things all together
in a freeform list of tags.)

However, if I knew that the tagging was based on a simple UI that clearly
explained the choices (such as the checkboxes proposed earlier in this
thread) then I would be happy to trust it and use it for making new ways.

Again this is different to tagging objects on the map.  If I see an object
tagged with building=apartments then it's pretty clear that the person doing
that tagging intended the same meaning I am thinking of.  For English speakers,
the tags are fairly self-explanatory.  Not so with something like 'foot'.
I have made GPS traces on foot which were not following footpaths at all, but
clambering over rocks.  So should they be tagged as 'foot'?  More to the point,
if I see a trace uploaded by somebody else tagged 'foot', can I assume that
they were following paths or not?  I really have no idea what they had in mind,
and the tag name by itself is not self-explanatory.  Without an agreed meaning,
tags are just junk data.

>I don't tag my traces because there's
>no point. If there was a menu I wouldn't bother because there's no point.

Personally, I can't see the point distinguishing between 'unclassified road'
and 'residential road', but I mark that distinction because there is an
obvious menu in Merkaartor which prompts me to do so.  Provide an easy way
for people to contribute, and they will do so.  Present them with a blank
textbox, and few people will trouble to go searching the wiki for appropriate
tags to use and their semantics.

>People will put tags in when it's either useful to them or
>useful to others.

People will put tags in when it's useful *and they are made aware of that*.
I never tagged GPS model used for traces because there was no prompt to do
so.  Until I saw house numbers on the map I never entered them - they would
have been useful, but I just didn't know that.

And of course, the more people enter information, the more useful it is.
Currently a few tags of 'foot' or 'car' on a few per cent of traces are not
useful.  Partly because there are few of them, and partly because you have
little idea what the person doing the tagging intended (see above).  Adding
a few suggested choices to the trace upload would solve both those problems.

-- 
Ed Avis <eda at waniasset.com>