[Tagging] Using multipolygons to map bays in Alaska

Daniel Koć daniel at xn--ko-wla.pl
Thu Nov 15 21:09:08 UTC 2018


W dniu 15.11.2018 o 12:08, Christoph Hormann pisze:

> The 'polygons is universally the preferred way of mapping no matter if 
> verifiable or not' and 'way_area equals cartographic importance' 
> concepts have been meanwhile extended to natural=strait in OSM-Carto - 
> thereby not only incentivizing against mapping with nodes but also 
> against mapping with linear ways.

Tagging both node and the area for bay is valid in documentation, so I
think this decision was also valid. It has nothing to do with
convenience, because we show both types, it's just how it's defined on
the wiki and we simply render all that is possible. The same is true
also for straits - according to documentation, they can be tagged as
lines in addition to nodes and areas. I hope we will add this rendering too.

You're using word "verifiable" as a final argument in such discussions,
but there are two big problems with it. First one is that you mix this
idea with idea of accuracy (and you seem to demand perfect accuracy).
The second one is that you suggest that such high call can dismiss
anything, while actual definition of verifiability is much different
than what you suggest - it's more subtle tool:

"Verifiability is an important concept to OpenStreetMap. OSM data
should, as far as is reasonably possible, be verifiable. This is a good
practice guideline covering all mapping activity, and also by virtue of
common sense, this has become a policy governing choices we make about
tags to use (and which tags gain acceptance)"

[ https://wiki.openstreetmap.org/wiki/Verifiability ]

Upon reading this definition it's immediately clear that:

1. It's just a good practice, which is a very helpful tool, but not a
hard rule (please read this definition too: "These >>Good Practices<<
are guidelines that will increase the quality and value of our map data
without any additional effort. Nobody is forced to obey them, nor will
OSM ever force any of its mappers to do anything." [
https://wiki.openstreetmap.org/wiki/Good_practice ]). It's weaker than
forbidding a copyright violations, for example.

2. Not everything is reasonably possible to verify, which means this
guideline has its limitations. If there is reasonable way to verify,
you're welcome to use it, if there is no sane way, just don't use it.
Simple as that.


> To be fair:  There are other map styles that do essentially the same so 
> it is not appropriate to exclusively blame OSM-Carto for this but it is 
> the only style that due to being rendered on OSMF infrastructure has a 
> true obligation not to do this.


Well, you try to frame what that obligation is and possibly enforce it
on the others - at least this is how I receive it. I don't agree with
such take and find it to be highly inconsistent with the documented
ideas (as verifiability and good practices), which you claim to be
defending.

Documentation talks about good will and does not give one true
interpretation, you talk about obeying and you give your interpretation
as a moral law, I guess. The spirit and wording is completely different
for me.


> Mapping bays with polygons is always non-verifiable to a large extent. 

Quite the opposite: it's verifiable to a large extent. Of course it's
not 100%, but more than 50% in the worst case. When one chooses the
border on the water it's just a common sense, but most of the bay border
is the coastline, which we accept as largely verifiable (even if it's
not true in all the cases).


> So the first thing you do with bay polygons for 
> generating quality labeling is to derive a node location from the 
> polygon and start from that - which makes the polygon drawing really 
> kind of insane.

That's perfectly sane that it's renderer job to take care of labels.
Database is not about labels, it's about describing objects. If you
don't like the node derivation for a label, you can derive line for it,
and you can do it in many ways. With node as an area replacement you
make one random, highly subjective decision for labels rendering, but
also for any other use like data analysis (as making stats etc.), that
does not belong to a data department.


-- 
"Excuse me, I have some growing up to do" [P. Gabriel]





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