-10 for adding defaults as a hint for mappers!!!
Every application using OSM data has to make assumptions about data not
present in the database, sure, but reliable data has to be present in
the database, as a missing tag in general can be both: missing/unknown,
or "default", whatever "default" means.
If we would define a set of defaults and mappers follow that set, nobody
will add "default" values again, and it's not possible to distinguish
between default and unknown any more.
Yes, sure: Applications should have these default values, and probably
it is useful to define some kind of "common defaults" in a file that can
be used and parsed by applications, but this should not be part of the
osm mapping work, but part of the software development around OSM (not
in the osm core).
regards
Peter
Am 13.04.2012 08:11, schrieb Colin Smale:
Yes please!
I was also thinking on the lines of documenting implicit tagging:
* to save mappers time
* to save space in the database
* to avoid confusion
* to allow a single point of maintenance
At a generic "territory" level with some kind of hierarchy please, so
for example cities can override counties which can override states
which can override national rules. As traffic rules are made by some
kind of government, I am sure the current boundary/admin_level stuff
can be used as a base as long as a true hierarchy can be found (no
multiple inheritance!)
<defaults territory="uk">
<defaultentry>
<match>
<tag k="highway" v="motorway" />
</match>
<implies>
<tag k="foot" v="no" />
<tag k="maxspeed" v="70 mph" />
<tag k="bicycle" v="no" />
</implies>
</defaultentry>
</defaults>
Technically it doesn't seem that difficult.
Colin
On 13/04/2012 07:27, Stephen Hope wrote:
The problem with this, is many mappers are not even aware of what
implicit assumptions they are making, and hence won't map them.
Saying that they should map them won't help.
Do we need a database* of explicit default settings for different
areas, to be used by renderers, routers and other tools as
appropriate? Rules like "In Germany, motorway implies foot=no if
there is no foot tag on the way". This could also help give sane
guesses of defaults for roads that haven't been tagged at all yet.
* either a separate database, or polygons inside OSM with tags,
whatever. That's not the point at the moment
Stephen
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