[OSM-talk] Relations not always brilliant

[Steve Hill]

On Sun, 6 Apr 2008, Richard Fairhurst wrote:

> In the UK, road numbers are unique (apart from about three cases
> where local councils have cocked up, e.g. the B4027)

This isn't entirely true - take, for example, the A31, which goes from 
Guildford to Winchester and then vanishes as it joins the M3.  It then 
reappears on the Westerly end of the M27 and continues to the West (the 
A35 does a similar thing, as do quite a lot of other A roads).

C roads, of course, are not unique (but their reference numbers tend not 
to be published).

> and no road can have more than one ref.

I believe that might also be untrue.  It doesn't excuse the use of 
relations though - multiple refs should be specified like: ref=Bfoo;Bbar

> The relation doesn't give any info over and
> above that in the standard 'ref' tags - it just increases complexity
> for both editing and processing.

I agree entirely.  Presumably the idea of the relation is to allow 
routing algorithms to rejoin ways which have been split, but this isn't 
necessary - if the end of 2 ways share the same node and they have the 
same ref then they can be rejoined.  The existence of multiple 
non-adjacent roads with the same ref doesn't change this and the existence 
of multiple refs for the same road only adds a minor complication.

  - Steve
    xmpp:steve at nexusuk.org   sip:steve at nexusuk.org   http://www.nexusuk.org/

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence