[OSM-talk] Good practice, and should we rely on defaults?

[Martin Koppenhoefer]

Am Mi., 6. Apr. 2022 um 13:59 Uhr schrieb Frederik Ramm <frederik at remote.org
>:

> Hi,
>
> my thought is that, in general, the default should not be added to OSM.
> For example, I don't want 95% of streets in Germany to receive a
> surface=asphalt or a motor_vehicle=yes!
>
>

yes, there are defaults and defaults. motor_vehicle=yes is a default that
is generally accepted on roads, in the absence of different access
information all highways are considered accessible and this is well
accepted. surface=asphalt is the accepted default in Germany for most road
classes, but for example with tracks or footways, if you don't have the
surface tag, it is not clear at all. Even with the combination of
tracktype=grade1 or 2, it could be interesting to distinguish different
surfaces, and no information here does not mean it is asphalt.

There are other defaults that are contested, for example lit on roads. Some
people think the default is yes (for example for residential roads), and if
you believe it is like this, you have to tag lit=no on the others, or it is
"no" and you have to tag lit=yes.

There is also the StreetComplete idea. The reasoning is, either you have
the information, or you don't and have to guess what is likely, but
basically have no clue whether it is the "default" or is missing the
information. Therefor they encourage people to add a lot of explicit
information from survey, that could have been guessed with a high
probability but still some uncertainty.



> (And I sure as hell don't want someone helpfully adding all those with a
> bot or a mindless editing campaign where mappers go "ah, what can go
> wrong, I'll just tag the default"!)
>


yes, this is also generally agreed I believe. If you do not know for sure,
have not verified, you should not add a piece of information, even if you
consider it very likely, as it would clearly lead to problems (those
unexpected exceptions would be hidden).




>
> For the same reason I am also opposed to mapping implicit speed limits,
> even though I see that that information can be useful in the absence of
> machine-readable regional defaults.



speed limits can only be inferred if you know the context. There are
others, but mainly the question is whether you are inside a settlement (as
determined by the traffic law, i.e. city limit signs) or not, which is not
an information that is generally available in OSM when maxspeed or its
derivatives are not tagged.

Cheers,
Martin
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