[Tagging] Another multipolygon question

Kevin Kenny kevin.b.kenny at gmail.com
Sun Oct 21 01:24:45 UTC 2018

> 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.

I actually do edit those things pretty routinely. It involves redrawing
only for the added ways.

Draw the new closed polygon representing the landuse=residential. Make it a
multipolygon immediately.

Insert nodes at the intersections of this closed way with the existing ways
(if you didn't draw it that way to start with). Split the old and new ways
on the nodes. (Splitting is safe - they're multipolygons already.) JOSM has
an 'add nodes at intersections' feature that helps with this.

Edit each of the old multipolygons to replace their old boundaries with the
new ones. That's just 'remove the old ways, insert the new ones' in the
relation editor.

Finally, delete any ways that are now unused.

I can do this *lots* faster than I can redraw an irregular boundary, at
least in JOSM. (I'm not skilled enough with iD to comment. it wasn't much
harder in Meerkartor when I tried it.)

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