[Tagging] Another multipolygon question

Mark Wagner mark+osm at carnildo.com
Sat Oct 20 19:10:54 UTC 2018

On Sat, 20 Oct 2018 09:49:57 -0500
Kevin Kenny <kevin.b.kenny at gmail.com> wrote:

> Not only legitimate,  but recommended!
> If you haven't stumbled on it yet, another useful procedure is to map
> areas of landuse use or landcover by drawing each border only once,
> and having each area be a multipolygon with the shared border way as
> a member. With that approach there's no need to retrace an irregular
> boundary. You just add it to the multipolygon on either side.

Works great, right up until you need to maintain it.  So, you've got
your "natural=wood" multipolygon sharing a way with an adjoining
"natural=scrub".  And then, some inconsiderate developer bulldozes his
way across the boundary and puts up a housing development.  Now what do
you do?  You can't unglue the boundary and shrink the two affected
areas to make room for the "landuse=residential" because there's only
one way.

The only option I've found is to remove the affected section of
boundary from one of the multipolygons, move it to the new location,
create a new boundary way for the other multipolygon in the proper
place and add it, create a new multipolygon for the development and add
the relevant boundary ways to it, and then confirm that you haven't
broken any of the multipolygons involved.  It's painful enough that
it's usually faster and easier just to delete everything and re-create
them from scratch as ordinary closed ways.


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