[OSM-talk] tagging roads

[Blaž Lorger]

On Sunday 02 August 2009 14:40:09 Pieren wrote:
> On Sun, Aug 2, 2009 at 1:39 PM, Blaž Lorger<blaz.lorger at triera.net> wrote:
> > 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.
>
> Adding narrow=yes to your unclassified highway meaning "it is 50% to
> 75% narrower than the usual unclassified highway width in my country"
> is universal and doesn't have to be added everywhere. When you add
> oneway=yes to a road, do you add oneway=no to all others ? When it is
> not attached, then it is the usual width of the unclassified highway
> in your country. And this can be used by any renderer who could draw
> thinner roads when the tag is present. But renderers will never draw
> the exact width=* of a road excepted at the very high zoom levels.

To my knowledge there is no such thing as usual highway width. There are 
certain standards for width of newly built roads, but those usually increase 
over time, which means you will be forced to periodically reevaluate *ALL* 
"narrow" tagging.
Obviously you haven't read my original message carefully. I suggested that 
only two widths are used by renderer and that border value is determined by 
renderer based on highway type.
Absence of width tag is interpreted as road having "usual" width. This is 
exactly same as absence of tag narrow.
Having actual road width is always more useful than having just some 
subjective estimate whether road is too narrow or not. Besides rendering you 
can use it to improve routing based on actual vehicle width/size.

>
> > 4. At the end it is always up to the individual mapper to decide what is
> > narrow. While 1 meter is 1 meter.
>
> You always have some subjectivity when you map, look the other thread
> about residential vs unclassified. Below you say yourself it must be
> estimated, so your 1 meter can be 1.5 meters for someone else. Your
> just give the "impression" that a number is more accurate than an
> adjective but it is just an impression (excepted if you really measure
> the width with a tape).
Well yes, but with "width" it is only estimation error. While with narrow you 
must decide what is usual width for specific type of road, you make estimation 
error for road width, you make calculation error in percentage of usual road 
width and you must decide whether calculated percentage width is low enough to 
justify narrow=true.
some subjective factor is inevitable, but at least it should be kept as low as 
possible.
Besides in case of dispute or for whatever reason, road can actually be 
measured. Whether road is narrow or not is always matter of opinion, there is 
no way to improve accuracy here.

> > 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.
>
> I only suggest narrow=yes. I don't understand what means
> narrow=foot|etc. It is narrower than the default width of the road. It
> has nothing to do with vehicules.
Again, what is default width of the road? And it has everything to do with 
vehicles, because what you need to now is whether your vehicle, which can be 
1, 2, 4 ... meters wide will be able to drive along road in question. 
Specifying narrow=yes|no can only be used to render a map.