[Tagging] objects mixing linear and area (for ex fence and landuse)

Kevin Kenny kevin.b.kenny at gmail.com
Mon Jan 18 16:32:40 UTC 2021

On Mon, Jan 18, 2021 at 11:18 AM Martin Koppenhoefer <dieterdreist at gmail.com>

> Am Mo., 18. Jan. 2021 um 16:54 Uhr schrieb Kevin Kenny <
> kevin.b.kenny at gmail.com>:
>> One thing that works wihtout wreaking any violence upon the data model is
>> to break the fence into two or more pieces and tag each piece with
>> `barrier=fence`. Then create a multipolygon with the lines as outer ways
>> and hang the description of the area off of that.
> I am already doing this, you do not even need to break the fence, the
> minimum requirement for a multipolygon relation is a closed outer way, one
> way is ok. It has the advantage that you can have as many attributes on the
> fence as you like (e.g. "height"), and it remains always "clean" and not
> ambiguous as with mixed objects. The actual situation is that they often
> have no additional attributes, so "fenced=yes" could replace them (although
> the ones without attributes might get them in the future, while those
> indirect "fenced=yes" objects have a higher probability to remain simple).

Without breaking the line, you have the issue that there are certain linear
features that can also be area features (or for which area semantics have
been requested) such as hedges. Breaking the way ensures that the feature
cannot be misinterpreted as an area just because it's a closed way.

The lines are simple linear features, so no data consumer has a problem
>> with them, and virtually all data consumers understand how multipolygons
>> work, so that doesn't cause a problem either.
> Yet there are many voices who do not like multipolygons, some time ago
> there was even a thread on User:Germany which suggested they were a
> disease. I can see how such a structure makes things slightly more complex
> and that as simpler solution with a property would be preferable - as long
> as it hasn't side effects.

As long as there are features with holes, there will be multipolygons. As
long as we have them, there is minimal harm in using them. Mappers will
need to learn them sooner or later.  In my arrogant opinion, the largest
single problem with multipolygons is that several editors don't really
handle them competently. I can work with them with ease in JOSM - and used
to do so in Meerkartor - but struggle with them in iD and never even tried
in Potlatch. This could, I concede, be my ignorance; it could be that iD
has better multipolygon features that I don't understand and haven't
troubled to try to learn. I'm fairly satisfied with editing in JOSM. It's
ugly, but it does what I want to do, and I don't insist on beauty.

73 de ke9tv/2, Kevin
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