[Tagging] Using multipolygons to map bays in Alaska

Peter Elderson pelderson at gmail.com
Thu Nov 15 14:19:36 UTC 2018

The rendering software would then derive the necessary quality information
from .... I don't know. Bay recognition software?

Op do 15 nov. 2018 om 12:11 schreef Christoph Hormann <osm at imagico.de>:

> On Thursday 15 November 2018, Dave Swarthout wrote:
> > [...]
> >
> > I was thinking it would be much easier and perhaps even better to
> > just draw an approximate shape consisting of maybe 20 or 30 nodes,
> > big enough to define the area and cause it to render, but easy to
> > draw and without involving any multipolygons. The issue here is
> > admittedly one I am pursuing to get these water bodies to render in a
> > manner proportional to their size and I suspect that many will be
> > against it on that basis alone. Still, I thought it worthwhile to
> > mention my idea here and see what you think about it as a "shorthand"
> > solution.
> I think it is good you bring this up because many mappers have been
> doing exactly that without asking - See for example:
> https://www.openstreetmap.org/way/548210592
> https://www.openstreetmap.org/way/544856564
> To put it right upfront:  This is a bad idea.  As you say the main
> motivation for doing this is to make a bay show up in the map.
> OSM-Carto has made the decision to incentivize this kind of mapping -
> and as i like to point out to derivate from its self declared goal to
> support mappers in consistent mapping towards steering mappers to map
> in a way that is convenient for style developers.
> 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.
> 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.
> Mapping bays with polygons is always non-verifiable to a large extent.
> Mapping bays with polygons as you describe it above is always
> completely non-verifiable and amounts to pure (low quality) label
> painting which should not be done and should not be incentivized by
> maps with a mapper feedback goal.
> If you want to generate high quality labeling for bays in maps what you
> need is the geometry of the waterbody the bay is part of (usually the
> coastline) and the location of the bay - which can easily be specified
> with a node in the way described on the wiki.  This allows for much
> higher quality labeling than a pretend-exact geometry either based on
> coastlines or not.  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.
> Long story short:  My suggestion is and has always been to map bays with
> nodes in those cases where this - together with the coastline -
> perfectly documents the verifiable information available on the
> geometry of the bay.  In other situations (which exist but are
> relatively rare) other verifiable modeling concepts can be considered.
> Drawing a coarse labeling polygon is not one of them.
> Links to previous discussion on the matter:
> https://lists.openstreetmap.org/pipermail/tagging/2014-October/thread.html#19775
> https://github.com/gravitystorm/openstreetmap-carto/issues/804
> https://github.com/gravitystorm/openstreetmap-carto/issues/2068
> https://www.openstreetmap.org/user/imagico/diary/43957
> --
> Christoph Hormann
> http://www.imagico.de/
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> Tagging at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/tagging

Vr gr Peter Elderson
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