2017-08-31 13:49 GMT+02:00 André Pirard <a.pirard.pa...@gmail.com>:

>    - The Belgian Flemish community wants to tag *maxspeed*=*
>    <https://wiki.openstreetmap.org/wiki/Key:maxspeed> on every road
>    instead of using a default. Is this a new specification and where is it
>    written? Must that now be done in every country?

We are doing this in Italy for many years now, and it is quite robust and
reliable. We are adding the source:maxspeed tags additionally to explain
whether the maxspeed is explicit (sign / road marking etc.) or implicit
(usually derived from a zone like "inside a settlement", "on a motorway",
"outside of a settlement", etc.). In all countries I am aware of you can't
reliably detect default limits without knowing if the road is inside or
outside of a settlement, which is typically not dependent on the actual
settlement but on street signs that tell you when you enter or leave a
(traffic code related) settlement. It has also proven useful for
maintenance and verification to map actual speed limit signs
(traffic_sign=maxspeed, maxspeed=n ) at the side of the road (to have the
direction stored).

Either the defaults are in the OSM database and it takes just a routinely
> map fetch to get them all updated timely,
> or each other router (GPS) writer implements them each their own way from
> various random other files. It's not well clear how contributors ca update
> all those files instead of OSM and it typically needs a full software
> update for each little default change, depending on writer's availability.

it really depends on the kind of "default" you are after. What about a
maxspeed=50 sign in Germany inside a settlement (i.e. it is a sign which
states the default). If the law for the default changes, this 50ies sign
will not have to change (unless they are going to modify the sign). If the
road is simply tagged with "highway=tertiary" you can't know whether this
is incomplete data, or the mapper had a lot of defaults in mind like
lit=yes, lanes=2, surface=asphalt, maxspeed=50, sidewalk=both, oneway=no,
smoothness=good, etc. (assuming a smaller road in a city).  You can't even
know whether the road is (legally) inside a city.

I guess you would have to define really complex defaults / processing to
cater just for the more used properties. A tag like source:maxspeed allows
to change all speed limit defaults in a country at once because they are
explicitly marked as defaults.

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