[OSM-talk] waist deep in the tagpile

Wed May 31 09:35:45 BST 2006

Jo,

Re "Map Features". A lot of the concern I had at the time I drafted it came
about because of ways. Ways are potentially very powerful in OSM in that any
selection of segments can be turned into a way and this way can have a
completely different set of attributes to any underlying segments or indeed
underlying ways. Thus "Map Features" was born to think in this format and
permit a large diversity of tags which would not be required more than once
as an attribute for any individual db element.

So I put together the "Map Features" listing as a suggested way forwards to
alleviate some of the restrictions that class=foo creates and to provide a
much fuller list of map attributes that editors can use. Non of it was set
in stone and the whole basis of OSM has always been to use whatever keys and
values you wish when editing so that, for instance, your bus map or pub
crawl map looks the way you want it to.

Having said that, there is a huge driver for having a consistent set of
"core" attributes that are there by default so that those wishing to create
basic map renderings can do so without having to edit the data themselves.

Etinene's Osmarender started off using the class approach, but he moved over
to the "highway" and full Map Features format some time ago. Nick's work has
until recently been mainly using the class tag but I think he has moved over
a bit too (haven't checked though). The editing applet still uses "class"
unless you type in something different yourself.

So for the majority of those editing who have yet to delve deeper, the
default values offered by the Applet are all they know. In JOSM it's a blank
sheet so you use what you like, I just happen to use "Map Features"
exclusively.

The result from my editing is that the whole of the West Midlands area (and
anywhere else I have been editing) is tagged almost exclusively with the Map
Features keys and values. I also make the vast majority of keys and values
on the "way" rather than "segment". Etienne I think tags the segments
predominately. I can't speak for others.

My personal view is that no key should ever be deleted as we have no idea
what a specific individual is using them for. The value for the key however
may be edited or changed as I think this is easier to accept.

So, for all those streets with a class key I would say at some point a
highway key ought to be added. Presumably it would be easy for a script (or
the editing software) to add certain keys and values magically when a user
adds certain key words (eg, for every class=foo pair added by a user a
highway=foo is added automatically if it does not already exist). This would
help those whose primary interest is in getting the OSM data out (rather
than putting it in)to create the sexy ways of having something amazing to
show off and promote the project...and themselves ;-)

The answer to a lot of these issues lies in the restrictions or default
feature set of the editing platforms. I would vote along the lines of the
Map Features format, although I have no problem with that being improved. I
placed a specific rider at the top of "Map Features" that it was an English
version of what was needed. I'm just not sure how my continental friends
view this in the context of tagging street in Sweden for instance.

Cheers,

Andy

Andy Robinson
Andy_J_Robinson at blueyonder.co.uk 

>-----Original Message-----
>From: talk-bounces at openstreetmap.org [mailto:talk-
>bounces at openstreetmap.org] On Behalf Of Jo Walsh
>Sent: 31 May 2006 02:35
>To: talk at openstreetmap.org
>Subject: [OSM-talk] waist deep in the tagpile
>
>dear OSM-ers,
>
>Chris mentioned that he, Schuyler and I have been experimenting with
>mapserver renderings of planet.osm imports, translating the XML dump
>into GML and thus via ogr2ogr into postgis/shapefile/etc.
>
>This has involved attempting to extract enough meaning from OSM's tag
>system to produce an Osmarender-equivalent view of what's in the latest
>dump.
>
>http://london.freemap.in/tagmania.html illustrates teh quandary that
>i find myself in. The tabs on the left show 2 different tagging
>schemes in effect, and what's been marked up with either one. (This is
>just the major street types, none of the footways/waterways/etc yet.
>This *doesn't* show ways, only annotated segments).
>
>In short, the "controlled vocabulary" suggested at
>http://wiki.openstreetmap.org/index.php/Map_Features asks users to
>annotate different classes of road with
>
>'highway = [some road type name]'
>
>By volume, more than twice as much data in May's planet.osm uses
>
>'class = [some road type name]'
>
>And in that heavily-annotated part of south-west london (kudos to the
>data gardener!) a stretch of the M25 is marked up with both keys.
>Planet.osm for May has 6888 segments that have both highway= and
>class= keys, and of those, 141 have different values for their keys.
>(Does this make sense? Does 'class' have semantics worth keeping?)
>
>Now, i've had one eye closed on OSM for a few months, and may well
>be missing a significant shift in peoples' labelling practises.
>I see two ways in which this situation could have arisen:
>
>1/ One set of people/clients is using 'class=foo', the other 'highway=foo'
>2/ At some point in time, most everyone agreed to shift from 'class=foo' to
>   the more human-compatible 'highway=foo'
>
>Asking onlist looks to be the only way to figure out which is the case;
>neither planet.osm or the API will tell me who tagged a segment, or when
>they did it. (I don't think a raw database dump would tell me either.)
>
>So right now, Etienne's wonderful Osmarender isn't picking up on the many
>segments that were tagged 'class=foo'. For the mapserver-based
>Osmarender knockoff i worked round this by making a duplicate layer for
>each key, that's what is shown in the map link above.
>
>What is to be done?
>
>* I leave things as they are, for others to workaround in the same way.
>  [ But this seems super-undesirable - the problem is small now. ]
>
>* I go through all the planet.osm segments that have 'class=' and no
>  'highway=' tags and POST additions to the API. I see no way to
>  delete tags through the API, this probably makes sense.
>  [ But this will lead to unnecessary data duplication + slowdown. ]
>  [ same issue arises with automated correction of obvious typos ]
>
>* I try to persuade someone with direct access to the OSM db to
>  replace all the class= tags with highway= tags.
>  [ But this may break the world of someone who is still annotating
>    with, or rendering with, 'class=foo' tags. ]
>
>* I ignore tagged segments and concentrate on ways
>  * But segments seem to have better metadata + presence than ways do
>  * Someone has to create the ways before they can get key/values,
>    either inherited from the segment's tags (again, do any of the
>    clients support this?) or re-created by hand.
>  * I worry that my understanding of how ways work is partial.
>
>While I'm here:
>
>- Andy's work on the Map_Features vocabulary is spiffing. Is this 'best
>practise' to the extent that it's implemented in one or more of the
>editing clients?
>
>On Tue, May 30, 2006 at 07:59:21PM +0100, Tom Carden wrote:
>> openstreetmap.org - the main site should always have the best possible
>> maps that can be generated from OSM data (it's behind at the moment,
>> but catching up thanks to Nick) because it's really the only place
>> that can drive traffic back to the editors.  Feedback is golden.
>
>- But not a cent for entropy?. The ideal of sensible shared
>classification emerging through demonstrated usage is a nice ideal.
>OSM has got to the stage where this has led to an evolved 'standard'
>which, though English-only, *is* being used in non-UK places in Europe.
>I think that entropy for key/value usage preference is missing now.
>"Most recently used popular tags" in an editing client could be a start.
>
>- Would a 'key foo is semantically equivalent to key bar, and value X
>in the context of key foo is equavalent to etc etc' be overkill? I
>mention it in the context of future i18n.
>
>- One thing the three of us have are planning for, is an AJAX editing
>client intended *only* for creation of metadata, not for drawing of
>shapes. But if something like this didn't run on the OSM systems, then
>we'd have to implement our own user authentication and either maintain
>locally a model of who-tagged-what-how-when and repost everything to
>OSM through one account, or somehow automate OSM account creation for
>everyone who came to use a tag-only client.
>
>The idea of a metadata-only client may sound dull, but i experimented
>with this a lot last year, before 'tagging' was implemented in the OSM
>API, and it had a lot of the same stickiness / 'just one more feature'
>compulsion nature to it as drawing clients do. Honestly ;)
>
>More than enough for now.
>
>
>jo
>
>
>
>
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