[Tagging] exit_to on motorway_junction

Colin Smale colin.smale at xs4all.nl
Sun Nov 18 21:34:23 GMT 2012

On 18/11/2012 21:59, Philip Barnes wrote:
> On Sun, 2012-11-18 at 21:26 +0100, Colin Smale wrote:
>> Phil, there's a difference between routing calculation (which neither
>> knows nor cares about road names, numbers, signposts etc) and how the
>> result of the calculation is presented to the user. Then you need to
>> relate the nodes/edges in the routing graph back to the real world. The
>> value in this tag (as well as name, destination etc) is that the
>> navigation software can give instructions based on recognisable
>> landmarks instead of referring to way IDs. This distinguishes between
>> pure "routing" and "useful navigation".
> Thats the point I am making, the most useful instruction a satnav can
> give is "leave the motorway a junction 4", or words to that effect.
> There is nothing more recognisable than the junction number.
Well, for a start junctions are only numbered on motorways and some 
trunk roads. I think most people would consider "keep left on the A1001 
towards Anytown" clear enough (assuming that's what's on the sign), with 
or without a junction number. There has also been a discussion going on 
(admittedly outside of the UK) about the use of destination:ref to store 
the ref of the destination, so in this case we would have 
destination=Anytown and destination:ref=A1001, plus junction:ref=5 or 
whatever. By structuring the information in this way we give navigation 
software the choice of how to present the data.


> Phil
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