[Tagging] Another multipolygon question

Dave Swarthout daveswarthout at gmail.com
Tue Oct 30 11:54:28 UTC 2018


Kevin,

Okay, I see understand the offset now and the reasons for doing it but wow,
such attention to detail is unusual in OSM mapping methinks. It was clever
indeed. I just began to use QGIS but I'm a complete noobie at it. My only
use of it so far has been to select and save into its own folder a single
shapefile (for a national Park or National Wildlife Refuge) from a monster
master file containing many individual shapefiles and even that took some
searching on Youtube before I could  pull it off. That is one powerful
program and learning how to use it isn't for the fainthearted. I love the
Adirondacks region and fear that at my age and physical remove (Alaska for
summers, Thailand winters) I'll never get a chance to hike there again. I'm
glad you are working to map that wonderful wilderness area.

Gosh, it seems I'll never run out of questions. Here's yet another.

Someone added the Arctic National Wildlife Refuge to OSM but did not add a
bunch of inner areas that aren't part of the refuge. I have the inners in a
shapefile that end up in a separate layer when I import them into JOSM. I
would like to add those inners to the existing boundary of the refuge. How
can I transfer those inners from the shape layer to my data layer?

I've tried everything I can think of, including the special paste function
inside the Relation Toolbox I learned about recently, but cannot get them
to transfer *en masse*. I can copy and paste them one at a time but there
are a few dozen tiny parcels. I also tried pasting them in place and then
using JOSM's Search function to select "type:way untagged new" and that
worked but it's clumsy.
There must be a better way to do this.

Thanks for your help, everyone.

On Mon, Oct 29, 2018 at 7:06 PM Kevin Kenny <kevin.b.kenny at gmail.com> wrote:

> On 10/29/18 2:48 AM, Dave Swarthout wrote:
> > But I'm still a bit confused about way:427547729. It's tagged as an
> > outer in the Wilcox WF multipolygon but it's located inside of an
> > enclosing way that's also an inner to the same relation. Does that
> > mean the inner/outer roles alternate as you add more and more "nested"
> > objects to the large multipolygon? For example,iIf there was a block
> > of private property inside way:427547729 would that be tagged as inner?
>
> You got it. That's why I chose that specific one as an example, to show
> how 'exclave within enclave' works. It's unusual, but it happens.
>
> > Just to touch on another topic because Kevin mentioned it. Sometimes
> > it's fairly obvious that certain boundaries were meant to follow a
> > riverbank or a coastline but at the present time don't. My first
> > impulse is to delete segments of the original boundary and replace
> > them with the more recent riverbank or coastline. That would probably
> > be considered wrong by some but seeing as we do not and can not
> > guarantee perfect accuracy with the placement of any boundary I don't
> > see it as an absolute no-no. Plus, many of these boundaries use
> > thousands of nodes that follow every little zig-zag to achieve legal
> > accuracy. IMO, OSM doesn't need that level of detail.
> >
> > Opinions?
>
> I think you're right about the level of detail, and in fact I simplify
> ways fairly often.
>
> Because partly of confusing advice here, in 'imports', in talk-us, and
> on the Wiki, when I did the reimport of the Adirondack protected areas,
> I did them as separate ways. In order to be able to simplify them, I
> used an 'erode' operation (a 'buffer' operation with negative size)
> where the size was slightly larger than the simplification tolerance to
> offset the ways before simplifying. At the time, I couldn't find such a
> beast in JOSM, so I used QGIS to do it.
>
> What happened to change my mind was further discussion here about
> administrative boundaries, and the way that the offset ways looked
> around the corridors that were cut out of some areas for existing roads
> and railroads. I've been sporadically changing the borders from offset
> ways to shared ways. You can see a partly-done example at
> https://www.openstreetmap.org/#map=16/43.8523/-74.2274 where the west
> side of Gooley Club Road is conflated and shared, while the east side is
> not. That's actually a 'not-too-bad' example since the Primitive Area
> corridor extends a hundred feet (~30 m) from the road centerline on
> either side. (Gotta fix the road designation, too - it's yet another
> TIGER Residential!. Grrr.) The corridor at
> https://www.openstreetmap.org/#map=16/44.0071/-73.9362 applies
> 'Primitive Area' protection to a three-rod right-of-way, and there was
> absolutely no way to get the ways simplified and aligned without
> conflating them (and in that case, why not make them a shared way?)
>
> I still think my approach was valid for the initial import, particularly
> since the boundaries in the source data were drawn so as to require
> manual conflation otherwise. I discussed this issue at the time in
> 'imports' and heard no complaints. In fact, one commenter thought that
> offsetting the ways automatically was fairly clever. For that reason, I
> haven't made the effort to go back and tidy everything. Still, if I
> happen to be maintaining an offset boundary for other reasons, I'll
> generally replace it with a shared way.
>
> > PS: This has been a most beneficial conversation. I feel enlightened.
>
> That's gratifying. The more people who understand how multipolygons help
> with this sort of thing, the more we'll be able to dispel the idea that
> they're unworkable or unmaintainable.
>
>
>

-- 
Dave Swarthout
Homer, Alaska
Chiang Mai, Thailand
Travel Blog at http://dswarthout.blogspot.com
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