[Tagging] Map maintenance with StreetComplete - Preferred tagging

Tobias Zwick osm at westnordost.de
Sat Jul 25 14:42:08 UTC 2020

> adding check timestamps as string tags for every single tag seems a lot of bloat. One tag per object for me would be acceptable because it is indeed a valuable information when something was last verified and no changes were necessary.

Definitely it has the potential for that. And as Mateusz noted in
another branch, check_date tags themselves could become out-of-date if
successive editors do not update the tag together with the tag it refers to.

On the other hand, at least at this time I do not see the danger of this
[=every single tag is accompanied by a meta-tag] happening, neither
through individual usage of such meta tags nor by being set by
StreetComplete automatically because only a small fraction of tags are
likely to change in a timeframe of some years or below. In other words,
only for a small fraction of tags it makes sense to attach a check_date
to. A good example of things that change more frequently would be
smoothness or opening hours.

For example one surveyor may check on-site the smoothness and surface of
a road, but not check if the width is still correct because he doesn't
have anything with him to measure it. Also, he doesn't want to check if
the speed limit is still correct because that would require him to go up
the road at least until the next big intersection to find a speed limit
sign (or not). He may also not want to check whether all(?!) the bus
routes are still correct. Generally, some information tagged on an
element is also not verifiable on-site.
What this example should illustrate is that it is illusory to assume
that a mapper is both able and willing to check everything at once for a
certain element.

(Basically, StreetComplete is founded on the idea that surveyors don't
have to tag and check "everything" at once for any given element but
add/update the information bit by bit.)


On the topic of map maintenance, there is another information that is
currently missing (from the API) which would be helpful to maintain an
up-to-date map. It is a bit off topic because this topic is mostly about
StreetComplete / on-site map maintenance but I would like to still touch
on it shortly:

If the date + *source* of the last change made on (the geometry of an)
element was readily available, through the API or another meta-tag
(source=bing, anyone? ;-) ), this would help to identify areas that
should be updated because a new more current and/or detailed source
became available.
In Hamburg, we are lucky that the public authority provides us with
really detailed up-to-date satellite imagery that are far beyond bing
but there is no easy way to see which buildings and road geometries have
still been mapped on the basis of bing and which are already using the
better source.
So in a nutshell, the topic of how to find things based on old sources
is also very relevant for remote mappers.


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