[OSM-talk] tagging roads

Blaž Lorger blaz.lorger at triera.net
Sun Aug 2 12:39:53 BST 2009


On Sunday 02 August 2009 12:36:48 Pieren wrote:
> On Sun, Aug 2, 2009 at 12:18 PM, Blaž Lorger<blaz.lorger at triera.net> wrote:
> > Wiki clearly states why tag narrow=yes would be a bad idea
> > (http://wiki.openstreetmap.org/wiki/Key:width#Using_relative_sizes).
> > Basically, what is wide for bicycle is narrow for a car, what is wide for
> > a car is narrow for a truck ...
>
> The wiki says "without clear definition" about narrow. We just need a
> clear definition on the wiki and mine is a proposal. It is just
> proportional to the default width for all highway types for all
> countries. The advantage is that you don't have to tag all highways,
> just the ones you consider narrower.
> Otherwise, if you use the width=x , you have to do it on all roads or
> it will never be used by any application since they don't know if this
> segment is wider or narrower than the 95% of the highways where this
> width is missing.
> Here we could start again the discussion about the default width or
> default lanes and so on per highway type per country. That's the
> advantage of the key narrow, it is easy to use for mappers and it
> works for all countries.

Let's see:
1. There is no clear definition what is narrow.
2. There is no specification for default width of road type.
3. If narrow=yes is not applied everywhere where it should be it is equally 
useful/useless as with width tag.
4. At the end it is always up to the individual mapper to decide what is 
narrow. While 1 meter is 1 meter.
5. Should definition of "default road width" ever change. All narrow=* tagging 
will be completely useless and will have to be reevaluated from scratch. 
Actually it will be useless before that due to subjective nature of value 
assigned to tag.
6. You will actually require large number of values for "narrow" to even 
approach granularity offered by one simple tag "width". Either you will have to 
have narrow=no|foot|bicycle|motorcycle|car|suv|lgv|hgv|... Vale yes could not 
be used, since it does not specify how narrow the road is or it could be 
equivalent for narrow=car.
7. You must prepare clear enough instructions how to select value for narrow, 
to reduce subjective factor to minimum.
8. You must get renderers to support it.

On the other hand, if you use tag width, which is already established tag if I 
may add, you have to accomplish following:
1. You must get renderers to support it.
2. Prepare some guidelines how to estimate road width. Of course using 
measuring equipment is always preferred but less realistic.
3. Deprecate tag est_width and always store width data in tag width. Add 
additional tag that would state accuracy of width data. This is really not 
necessary, but will be easier to use by the software and probably also easier 
to map.





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