[OSM-dev] likenesses

[Richard Fairhurst]

SteveC wrote:
> I want to revive a very old idea - tag equivalences. It might be  
> solving a problem that doesn't exist or someone might have done 
> it and I've missed it.

Wow, lots of issues here. And since

> I'm not a socialist moral relativist

...I am, almost, then I get a head-start on this one. :p

I'm generally with Eugene in agreeing that the words don't mean anything.
Perhaps the best example is highway=trunk. That was invented over here
(*waves at Andy R*) but we don't use it for UK trunk roads. We use it for UK
primary routes. Non-primary routes, we tag as, er, highway=primary.

This can only increase as editors increasingly abstract tagging away from
the keys and values. I've even seem some screenshots of some upcoming editor
or other with these lovely clickable icons with little cars on them - don't
know if you've seen that one?

So motorway or autobahn - meh. It's just words.

But, that aside: yes, we should do it.

We have all sorts of 'implied' tags. highway=motorway implies foot=no and
bicycle=no. junction=roundabout implies oneway=yes. And yes, anything (well,
except name maybe) =true implies =yes.

We also have implication by area. highway=motorway on a road in the UK
implies maxspeed=70mph, whereas in France, it implies maxspeed=110.

Implying things is good, because we optimise for the mapper, not the client.
It does mean the client needs to figure all this out. I've long said we
should (sorry) have standard libraries talking to some sort of dictionary
with all this in: as a first step to a dictionary, the other year I started
(not machine-readable)
http://wiki.openstreetmap.org/wiki/Key:highway#International_equivalence
which has been taken up by a bunch of other people and is, really, the only
sane description of highway types we have. But it's not machine readable.
This looks like the same kind of idea but machine readable, so, yay. Apart
from the XML bit. ;)

cheers
Richard
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