[Talk-us] natural=* and landuse=* multipolygons at the urban interface

Steve Friedl steve at unixwiz.net
Sun Aug 13 23:34:00 UTC 2017

You’re referring to the Scrub From Hell.

I (user SJFriedl) have been mapping extensively in Orange County and (especially) in the Santa Ana Mountains and this thing is *everywhere*. Not patches here and there, but everything everywhere is part of one enormous scrub relation and it’s positively maddening.

Even if you’re not trying to fix the big problem you’re describing, just cleaning up a boundary somewhere by adding a few nodes runs over the limit for a way (6k-ish?) and *boom* now you have to deal with the big picture. Ugh.

At the time I was most interested/frustrated in this, I didn’t have nearly enough chops with relations to give it a go, but after I fully relationalized all the city boundaries in Orange County, I’m game. JOSM is great.

You’re right that splitting this up is the right approach, because I don’t believe having all this as one huge relation was every the right thing to do as I cannot see how the related-ness of all the scrub patches in a very wide area is useful information (the scrubs that are part of the relation are not any more “related” than standalone patches of scrub in the same area).

There for sure are legitimate agricultural lands in OC, but they’re mainly in the foothills of the mountains; I’d not expect to see much grazing in (say) Ladera Ranch.

I’m glad I’m not the only one who’s noticed this :-)

Steve – who lives in Tustin

Stephen J Friedl  | Security Consultant | UNIX Wizard | 714 345-4571
steve at unixwiz.net | Southern California | Windows Guy | unixwiz.net

From: David Kewley [mailto:david.t.kewley at gmail.com] 
Sent: Sunday, August 13, 2017 1:12 PM
To: OpenStreetMap talk-us list <talk-us at openstreetmap.org>
Subject: [Talk-us] natural=* and landuse=* multipolygons at the urban interface

Development in Orange County, California pushes into areas currently covered by polygons (often large multipolygons) tagged as natural=scrub, landuse=meadow, or landuse=[farm|farmland]. These were part of the FMMP import http://wiki.openstreetmap.org/wiki/California_Farms.

Mostly I try to leave those large multipologons alone, because I don't feel confident I can handle them properly, and because I'm using iD (due to using a Chromebook), where relation handling is rudimentary.

But I'd like to update the urban-wildland boundary, where new suburban developments are pushing into former wildland, farmland, or (historical?) "grazing land". See for example the new development (with 2017 imagery recently added to Bing) at http://www.openstreetmap.org/edit?editor=id#map=16/33.5352/-117.6034.

Editing these huge multipolygons, and reviewing others' edits to them, becomes very cumbersome, at least to me. It seems to me probably sensible and reasonable at the urban edge to split off small parts of these multipolygons, e.g. at roads, to make the smaller bits easier to edit and review in the context of the expanding urban edge.

As one test / demonstration edit (http://www.openstreetmap.org/changeset/51090963), I carved off a bit of natural=scrub from a large outer role of a multipolygon, into its own polygon. I manually added new boundary way segments, stitched them together into the existing ways, copied tags, and made the split-off piece its own polygon, independent of its original parent multipolygon. I did the split at an existing highway=residential object (Golden Ridge Lane).

I know, I should find a way to use JOSM, which I expect makes this much easier. :)

Meanwhile, does this seem a reasonable approach to making the urban interface a bit more manageable in the future? I.e. splitting off parts of large multipolygons (so long as they don't have names or other unique identifiers that matter, just generic tags things like natural=scrub), to make future editing easier?

I know for the above example of a new residential area, I could make a landuse=residential island, and make it an inner role in the surrounding landuse=meadow multipolygon. But at some point as the urban sprawl expands, it seems to me it makes more sense to stop pretending the area is dominated by the natural features, and make it clear it's dominated by e.g. landuse=residential, with possibly interspersed natural features like scrub.

What would the group suggest?

Is my test edit reasonable, or should it be reverted?


P.S. As an aside (not my main point today), the FMMP-based distinction in this area between scrub and meadow seems awfully arbitrary. I could be mistaken, but I don't believe the "meadow" is actually used today for grazing nor feed harvesting, and in the aerial photography, it appears indistinguishable from the adjacent "scrub". It appears (and I'm nearly certain from driving by) that there's both substantial grass and substantial woody plant cover, in similar ratios in both "meadow" and "scrub".

I don't believe there's any current agricultural use of that land, at least not near where I'm giving examples today. There might be some large-acreage, semi-wildland grazing or feed harvesting activity remaining in Orange County, but I've not noticed any.

As documented in the FMMP wiki page http://wiki.openstreetmap.org/wiki/California_Farms, the FMMP designation "Grazing Land" was mapped to landuse=meadow.

But the FMMP designation of "Grazing Land" explicitly does not mean that there *is* grazing activity there, just that it is "...land on which the existing vegetation, whether grown naturally or through management, is suitable for grazing or browsing of livestock." (See for example http://www.conservation.ca.gov/dlrp/fmmp/Documents/soil_criteria.pdf.) So wildlands that will never again see livestock, or harvesting for livestock feed, can still be designated Grazing Land by FMMP. Those areas map better to natural=grassland or natural=scrub, I think.

So landuse=meadow seems less useful than natural=scrub or natural=grassland for many of these areas. Even though this is a secondary point today, I'd welcome comments on this as well.

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