[OSM-talk] OpenStreetMap routing service

[Ben Laenen]

On Monday 08 September 2008, Nic Roets wrote:
> On Mon, Sep 8, 2008 at 3:23 PM, Lars Aronsson <lars at aronsson.se> 
wrote:
> > Here you assume that "trunk" is a well defined concept.  But it
> > isn't.
>
> Spot on.
>
> And defining things per country leads to all sorts of problem. For
> example mappers applying domestic rules when visiting foreign
> countries. Confusion when debugging routing software. Next mappers
> will omit units of measurement because they feel it it's implied for
> their country.
>
> The solution is for editors to create defaults for these disputed
> access restriction tags and allow users to change them before
> committing them to the database.

I strongly disagree. There are so many country specific rules that it'd 
be naive to think you can twist everything into one system that applies 
world-wide.

If you're in a country where trunk means a road where no pedestrians or 
cyclists are allowed, then adding that information in the database is 
unnecessary. This makes sure that
(a) if for some reason the traffic rules change so that the sign marking 
that kind of road allows pedestrians, we don't have to edit all trunks 
in a country, and
(b) it fixes the problem where someone might not be familiar enough with 
the traffic rules so he doesn't know for example that pedestrians 
aren't allowed and doesn't add that access tag.

We've had a similar issue like that recently on talk-be, where mappers 
didn't know the exact meaning of a sign. Something tagged with a sign 
for access=destination in Belgium means: no entry except to the houses 
or fields in that road, and except pedestrians, cyclists and horse 
riders (and a few more exceptions that don't matter here). 
The "pedestrians" part is obvious to anyone over here, the latter two 
aren't. Indeed, you can even find those signs now and then that have a 
redundant "except bicycles" sign under it, so the people putting up 
those signs aren't always aware of that either.

Now suppose that access=destination would just have the world-wide 
definition so it wouldn't exclude bicycles or horse riders. If our 
mappers don't know the exact meaning of the traffic sign, it would mean 
that all routers would steer you round these access=destination roads. 
So, therefore we can better define this by country (or perhaps state in 
some cases), where the rules are actually made, so this problem won't 
happen.

Greetings
Ben