[Tagging] Rock outcrops in forest
osm at imagico.de
Mon May 28 12:50:41 UTC 2018
On Monday 28 May 2018, Ture Pålsson wrote:
> > landuse=residential and landuse:secondary=retail is what is
> > happening on the ground in some places.
> Random thoughts:
> Does this really buy anything compared to overlapping polygons
> (except, obviously, where the polygons are coincident, in which case
> it saves a polygon)?
It was not my intention to push this idea here or to advocate a
particular use case. If you as a mapper find it useful then use it,
But creating two separate geometries to document different properties of
the same real world objects, like the ground conditions in a
wood/forest, is both pretty pointless and against OSM principles. And
semantically it is not clear in such a case which geometry represents
the primary characterization of the area (what the area *is* so to
speak) and which is a secondary characterization.
In general the meaning of overlapping polygon geometries is - with the
exception of some situations where both geometries are clearly on
different semantic levels - fairly undefined in OSM. In many map
styles including the standard style most land based area types that are
rendered are sorted by size meaning that small polygons are interpreted
as superseeding large geometries in meaning if they overlap. But this
is not a rule you can rely on. So as a general rule for mapping: If
you want to be clear and non-ambiguous you should typically avoid
overlapping geometries of different feature types of the same or
similar semantic levels.
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