[Tagging] 'ongoing' U-turn restriction

Colin Smale colin.smale at xs4all.nl
Thu Dec 8 18:13:58 UTC 2016

On 2016-12-08 15:12, Martin Koppenhoefer wrote:

> On 8 Dec 2016, at 12:25, Colin Smale <colin.smale at xs4all.nl> wrote: 
>> Martin, your interpretation is jurisdiction-dependant. There is sometimes a distinction between single and double lines as well (Queensland is an example I just found). The objectively verifiable fact is the road marking, thereafter you have to interpret the local laws to understand its effect.
> Yes, if you map with the divider tag you don't have to understand the meaning, your direct uneducated observation is sufficient for mapping, still I'd consider the resulting effect from interpreting the local law something "objectively verifiable" as well - and more interesting for OSM if there are significant differences in meaning. Usually we do add our interpretation (e.g. the access rights of a road, put on the highway) rather than limiting us to pure physical facts (e.g. an access restriction sign), and we clearly prioritize the former.

Absolutely! But we need more subtle nuances in our tagging - "no
overtaking" is too broad IMHO. As has been mentioned many times before,
this is a case where we could benefit from a curated database (in
whatever form!) of semantic implications based on geographic areas, so
we could suffice with tagging the divider and any other road signs (as a
physical fact) and have a clear set of rules which these facts imply.
For example if we have divider=single_solid_line the database may
contain rules for all the different states to state what that actually
means. In one country it may be "no overtaking", in another it might be
"no crossing the line except to take a turn". If we develop an explicit
tagging scheme for all these nuances, this database could be considered
"defaults in the absence of explicit tagging to the contrary". But now I
am being rather heretical and at risk of being burnt at the stake for
mentioning documented defaults.... 

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