[talk-au] tagging 4WD and dirt roads - want it ?

David Bannon dbannon at internode.on.net
Sat Nov 10 22:31:40 GMT 2012

On Sat, 2012-11-10 at 14:54 +1100, Andrew Harvey wrote:
> ......
>In summary, I would ask you to pull out attributes of a thoroughfare
> which make it 4wd only and tag those instead.

Andrew, thanks for the very carefully considered response. 

I agree with just about all the points you make but suggest your
conclusion may not quite address the driver for this proposal. This is
about getting knowledge into the hands of end users. Safety is a key
factor, I am sure you heard someone died on an outback track only two or
three days ago.

What I am trying to do is get a reasonably easy to understand and use
model in place so mappers put data into the database in a consistent way
and, critically, the rendering people and the routing people use it. At
present, we have a large number of tags that relate to this space but
the only one the renderers use is tracktype. They ignore
surface=unpaved, 4wd_Only, smoothness= and so on.

Your suggestion, that we focus on specific characteristics of the road
and describe them is a good thing and one I'd support if you were to
start working on it as a proposal. But it does not apply here.

While having breakfast I could easily think of ten items I'd like to add
to your list of road characteristics, I'm quite sure that if we sat a
few more 4wders around the table we could hit twenty in no time. If we
convert them all to tags we'd have two real and pressing problems -

1. Mappers could not cope with that many tags to address in a consistent
way, even if they did, think of the extra data that would be, in many
cases unnecessary. Subsequent validating of such a fine grain data would
be a daunting task.

2. Importantly - it would be impossible to get the rendering people to
even consider displaying such a range of data. And if the mainstream
rendering engines don't show it, the routing people ignore it. Truth is,
when an end user uses OSM to decide to go a particular way, he/she does
not fire up JOSM and examine the tags on each way, they look at a map,
or, worryingly, rely on a routing tool.

I believe we need something simpler, something that is an extension of a
tag that is already rendered, for example on the OSM website. Yes,
tracktype does focus on compactness at present but thats because in the
range of roads it currently addresses, thats the issue. I propose we
extent that range of roads.

WRT the mention of "bad data that needs to be fixed", you must note that
this proposal does not make that issue any worse, indeed, by focusing on
one linear tag, tracktype, it might actually help. The problem is not
strictly linear but can be projected onto a linear tracktype scale at
the granularity proposed given the sort of knowledge any reasonably
experienced 4wder has.  Importantly, it's better than nothing and that,
I am afraid, is the likely alternative.


> Furthermore, the current tracktype grades although not well defined
> essentially measure the "compactness" of a surface. If you try to bring
> 4wd only into the mix it could become complicated as you can very well
> have paved track or heavily compacted hardcore but so uneven and with
> large gaps that you would need the large wheels and ground clearance of
> a 4wd to traverse; yet have another unpaved uncompacted track with lack
> of hard materials with the same requirement on a 4wd due to uneven
> ground. This isn't as you suggest, "bad data that needs to be fixed by
> mappers."
> In summary, I would ask you to pull out attributes of a thoroughfare
> which make it 4wd only and tag those instead.

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