[Tagging] Tags useful for rendering of roads in poor conditions

[Matthijs Melissen]

On 2 January 2014 16:15, gweber <gweberbh at gmail.com> wrote:
> I would strongly favour a simple dashed border style whenever the surface
> tag falls into the unpaved categories. It is as simple as that. From my
> experience in driving on rural roads in Brazil, nothing else is required.

The disadvantage of using the surface tag is that the category of
unpaved values is not closed. There are currently 147 surface tags.
including surface=sandstone, surface=metaled, surface=timber,
surface=rubber, etc. It can be expected that the number of surface
types will keep growing, and renderers and routers can't really be
expected to keep up with all the new unsurfaced types. So some unpaved
tags will necessarily not be supported.

This is a general problem with keys with open, unstructured tag
values. Although such keys allow for fine-grained mapping, they are
often useless to systems that interpret the data. For example, one
could tag a bed store with shop=furniture, which is interpreted by
some data consumers. One could also refine it and use shop=bed, which
might be an improvement in terms of data accuracy, but it also means
that most data consumers won't be able to interpret the tag anymore.
Adding explicit structure might be a solution, for example by using
shop=furniture, furniture=bed. In general, I think that open,
unstructured tags are a bad idea for this reason.

In any case, using the surface tag seems to be not ideal. On the other
hand, I do also agree with the criticisms on using tracktype.

Would there be any alternatives?

One thing I can think of is to introduce a new tag paved=yes, and to
use this to decide rendering (and perhaps routing). It would mean a
lot of extra tagging, but on the other hand, if the renderer supports
it, I believe that that might happen quite quickly.

Alternatively, we could stimulate users to restrict the surface tag to
paved and unpaved, by rendering only surface=unpaved and no other
values. We could then propose additional paved= and unpaved= keys to
specify the type of underground.

Another question is whether to use paved or unpaved as default.
Probably, paved is the correct tag for most of the world, as in a
large part of the world, most roads are paved. However, we should take
into account that this still risks bringing lives into danger, perhaps
even more so than in the current situation. Imagine a map where one
road is mapped as dashed, and another as non-dashed. This leads the
user to believe that the non-dashed road is paved, probably even more
so than in the case where no road is drawn as unpaved. Due to lack of
data completeness, of course the non-dashed road might still be
unpaved. Do you think this would be a problem in Australia or Brazil,
for example?

-- Matthijs