[OSM-talk] tagging roads

[Martin Koppenhoefer]

2009/8/3 Blaž Lorger <blaz.lorger at triera.net>:
> On Monday 03 August 2009 12:18:14 Emilie Laffray wrote:
> We generally agree that there needs to be a way to assure quality of entered
> data. Using two distinct tags for measured and estimated values (width and
> est_width) is one possible approach. But in my opinion it is not the right
> approach:
>
> a. You must be careful when entering the data to use appropriate tag. It is
> easier to use tag width in place of est_width. So most people will probably
> use width instead of est_width.

this might be true, but most probably people won't tag any width when
just mapping superficiously. I agree that it would have been better to
have width for the estimated width and something like "precise_width"
or "measured_width" for measured values.

> In such dual tag approach using tag width for
> estimated width and measured_width for exact width is likely to give better
> results, since people that put more effort in gathering data are more likely to
> put more effort in entering such data in database.

+1

> b. But dual tag approach is also problematic for software that uses data.
> Either software has to use exact value with fallback to estimated value, or
> more likely, software will only use one value and ignore the other. This in
> turn will likely cause that mappers will use tag supported by software
> regardless if their data is accurate or not.

maybe you should be more confident in the others ;-). I don't think
that most of our width-tags is useless because unprecise or badly
estimated.

> What I'm proposing is to add additional quality assurance tags. Absence of
> such tags would mean that there is no way to know how accurate data is. But
> presence of such tags would give reasonable assurance on data quality. I see
> need for two such tags: measurement method and date of data acquisition.
> So, when road width is just roughly estimated mapper would add only tag width.
> When road width is actually measured, tagging would look like this:
>   width=6.5
>   width:method=tape
>   width:date=2009-07-23
> When width is measured on aerial photography method could be aerial and date
> would be date when photography was taken, ...

actually there is already some people using tags like source and note
to add this kind of information. But they are few I guess.

> This approach can be used with all values that require measurement. It gives a
> way to quickly gather rough and inaccurate data with a way to identify
> inaccurate data, so it can be improved upon.

IMHO good idea. Did you check if there are already proposals to tag
this kind of datum? Of course also tags like can never make sure, that
they don't end up at some other way (someone copies the tags to
another way, some roads are combined, etc.), but they promise to have
information about the source.

>> > 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.

yes I agree, "narrow" does not seem to be a appropriate tag to tag the width.

cheers,
Martin