Defaults would have to be set nationally or regionally.
My TagCentral proposal would address this.
http://wiki.openstreetmap.org/wiki/SotM_2010_session:_Tag_Central:_a_Schema_for_OSM
I really must get round to doing something about it.
David
On Monday, November 1, 2010, Colin Smale <colin.sm...@xs4all.nl> wrote:
> On 01/11/2010 19:36, David Earl wrote:
>
> On Monday, November 1, 2010, Andy Allan<gravityst...@gmail.com> wrote:
>
> On Fri, Oct 29, 2010 at 9:52 PM, Colin Smale<colin.sm...@xs4all.nl> wrote:
>
> On 29/10/2010 22:22, thomas van der veen wrote:
> You might like to take note that nothing is implicit in OSM. There are no
> "defaults" as renderers or other consumers of the map data are unconstrained
> as to how they handle missing tags. Ideally all roads should have maxspeed
> explicitly tagged, even if it could be implied from the road class or other
> information.
>
> I disagree quite strongly on this. I see little point in pointlessly
> adding tags when they there is a sensible default. For example, we
> don't need to tag 98% of roads as "oneway=no", and in the same way we
> don't need to tag 98% of UK residential roads as "maxspeed=30mph".
>
> Life's too short for that kind of tedium. That's why we (actually do)
> have implicit information in OSM.
>
> +1
>
> David
>
>
> I agree with you both too. I was merely stating (for the benefit of a new
> mapper) that there is no working system of defaults. It would be very helpful
> if such a thing were to exist, but right now, there are no defaults.
> "oneway=no" is a bit of a no-brainer but the majority of "unwritten rules"
> ("implicit information") are not quite as obvious. In some cases, the wiki
> states that certain tags may be implied from others (e.g. highway=motorway
> implies oneway=yes) but these are, in general, poorly documented and
> information is fragmented and not easy to find. A welcome exception is the
> wiki page covering access tags for different highways[1]. Renderers or other
> "users" are just as much free to do their own thing as mappers are. The only
> thing that stops the whole shooting match descending into chaos is a set of
> agreements between producers and consumers. If it's not written down, and
> communicated appropriately, it might as well not exist. If you want to be
> unambiguous, use an explicit tag.
>
> So why not start documenting all these defaults or implied values? Here's a
> few suggestions to get the ball rolling.
>
> highway=motorway implies oneway=yes, lanes=2
> highway=*, oneway=no implies lanes=2
> highway=* AND lanes>=2 AND oneway=yes implies maxspeed=70mph
> highway=* AND lanes>=2 AND oneway=no implies maxspeed=60mph
> highway=* implies maxspeed=60mph
> highway=residential implies maxspeed=30mph
> junction=roundabout implies oneway=yes
>
> Colin
>
> [1]
> http://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Access-Restrictions
>
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