[Tagging] works_as_highway=primary

moltonel 3x Combo moltonel at gmail.com
Tue Jul 28 15:29:10 UTC 2015

On 28/07/2015, Marc Gemis <marc.gemis at gmail.com> wrote:
> On Tue, Jul 28, 2015 at 4:14 PM, moltonel 3x Combo <moltonel at gmail.com>
> wrote:
>> That ideal doesn't match the practical reality. highway=primary has a
>> very different definition between Ethiopia and Germany, by necessity.
> While they can be very different, a router should still be able to prefer a
> primary road to navigate you from city A to B and avoid secondary or
> tertiary roads. Of course in Germany it might be a smooth asphalted road
> and in another country a sand road, but that doesn't matter.
> Are the current router properly routing over the Irish roads ? Can they
> properly deal with the classification changes ? Or are those changes
> ignored because the speed limits are properly tagged.

I was arguing against a worldwide unified classification. What you're
worried about is only local classification :

A router won't care about classification differences between far away
places like Germany to Ethiopia. They just care about taking the best
road in the area, and as long as OSM is locally consistent, this
works. Even if a trunk turns into a primary for no physical reason and
without additional helpfull tags like maxspeed, a router likely won't
be thrown off and avoid the primary, because there's nothing better
than the primary_which_used_to_be_trunk around.

One routing error that came up recently is a trunk with a lower than
typical maxspeed, and a trunk_link without a maxspeed tag. The router
used its default idea of maxspeed for that link, and tried to use it
as a shortcut. The router could have been smarter, but the data should
have been more complete too, adding a naxspeed tag.

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