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

[Mateusz Konieczny]

Apr 6, 2022, 13:54 by 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!
>
> (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"!)
>
> However, there can be situations where these tags could make sense even in Germany, for example when there's a little piece of asphalted road in the midst of cobblestone segments - I would definitely put a surface=asphalt there to avoid someone else coming along and thinking "ah, this little gap in the cobblestone is surely there by accident..."
>
> We need to establish good ways to make country-wide (or region-wide) defaults available in a machine-readable way. Tagging those defaults onto every single object in one country because the default in this country might be different from the default in the next country would (a) create too much data inflation and (b) mean an edit orgy every time the default changes in a place.
>
In my experience both (a) and (b) is not some serious problem.

For (a): it kind of depends on what kind of things would be tagged, but in my opinion:
- putting maxweight:signed=no on most of roads on bridges is not some big burden
and worth it if it allows to coordinate and find 1 previously unmarked weight limit
for every 100 maxweight:signed=no added
Disclaimer: I added this StreetComplete quest (and during testing I found several missing
weight limits on bridges, in area that I considered as extremely well mapped)

- placing explicit surface on all ways is a good idea and worth it to catch rare
roads which are not surface=asphalt (avoiding sand and cobblestone is critically
import while cycling - and such tagging allows systematic verification of all roads,
otherwise coordination between mappers is hard to arrange at best)
(here I found with StreetComplete some sett/cobblestone roads which were
not known to me)

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For (b):  this defaults change really rarely, and if tagging is well designed then it
is easy to change - or maybe not requiring edits at all!

Poland changed implicit urban speed limits (dropping increase to 60 km/h during night)
and it was trivially solved by bot edit
https://wiki.openstreetmap.org/wiki/Automated_edits/TTmechanicalupdates/Remove_night_time_conditional_speed_restriction_in_urban_areas_in_Poland

It was a tiny project and not a big challenge.

And if it would be tagged with maxspeed:type=PL:urban or similar it would not even
require editing.

And if default for say surface=* would change - that is rather reason to mark it explicitly.

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> 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.
>
How would you distinguish "urban implicit speed limit" and "rural implicit speed limit"
without that?

At least in Poland areas signed as urban speed limits are different from any administrative
areas. And from landuse=residential areas.

(other countries may have similar differing implicit speed limits which also require survey
and are not guessable with any decent accuracy)
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