[Tagging] Urban perimeter

Fernando Trebien fernando.trebien at gmail.com
Tue May 27 15:53:34 UTC 2014

Yes, in Brazil that is a legal definition. That's why it will often
not correspond to areas marked using landuse=*. You may find farms on
the urban side of those limits (whose residents pay taxes under the
urban tax system), and dense urban settlements on the outside (whose
residents pay taxes under the rural tax system). This often happens
when the legal definition has not been updated to reflect reality. As
I said initially, in Brazil it also determines what environmental
policy is followed by authorities.

The "urban perimeter" is a "major factor" used by transit authorities
to establish maximum speeds, but not the only criteria for that. So
yes, you do find a few high speed highways on the urban side and a few
low speed areas on the rural side, but these are the exceptions
(usually where a new urban cluster is forming within a municipality
but is still dependent on the municipality's local government).

Several similar (not equal!) concepts I've found, but with different
- urban growth boundary: https://en.wikipedia.org/wiki/Urban_growth_boundary
- urban (UK)/urbanized (US) area:

Would I reuse the existing nodes or share relation members with
landuse=residential/*? Only if they're sufficiently close/similar (as
I would with any polygon/multipolygon out there). But they're
certainly not the same thing.

If all landuses are already mapped, in a country with no such similar
legal definition, the "perimeter" could probably share nodes/ways
along the outermost border of individual landuse=* clusters. I think
it would not be a collection of such areas, though it could be and
then the user would be required to merge all areas down (and possibly
fill in holes) to obtain a similar result. (In fact, I think this is a
more generic concept than that of the legal definition in Brazil; if
this already existed in OSM, we would probably adapt our definition to
it without trouble.)

On Tue, May 27, 2014 at 11:27 AM, Pieren <pieren3 at gmail.com> wrote:
> On Tue, May 27, 2014 at 3:37 PM, Fernando Trebien
> <fernando.trebien at gmail.com> wrote:
>> I like Nelson's idea of using a new value for "boundary" to represent
>> this, mainly because the perimeter is not "ground truth" but an
>> invisible "legal definition" that roughly matches the urbanized area.
>> I was wondering if this concept exists elsewhere so that we can even
>> propose such value in a way that's reusable worldwide.
> That's the point. Is it "legal" or just the sum of all urbanized
> "landuse" 's (residential, industrial, retail). Does it include
> backyards, garden, orchard, etc ? The limit is often clear on the road
> (first/last building + road sign) but fuzzy on aerial imagery if you
> want to draw the area. And if all landuses are already mapped, do you
> add a new polygon reusing existing nodes or do you create a
> multipolygon relation (splitting the existing landuse) or you just
> collect the sum of existing landuses ?
> Pieren
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Fernando Trebien
+55 (51) 9962-5409

"Nullius in verba."

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