[Talk-us] Gluing boundaries to roads (was Talk-us Digest, Vol 31, Issue 1)

[Alan Mintz]

At 2010-06-01 06:00, Lord-Castillo, Brett wrote:
>I don't think I have encountered a situation where an administrative 
>boundary at the city level of higher follows a road (i.e. if the road 
>changes alignment, the boundary changes alignment). Sometimes boundaries 
>below the city level are defined by roads, but those are not legally 
>defined boundaries. There occasionally are legal boundaries defined on a 
>river, but only if the river changes course gradually and naturally. If 
>there is a radical (e.g. a post-flood cutoff of an ox-bow) or man-made 
>(e.g. a dam causes flooding that shifts the midline), the boundary stays 
>fixed at its original boundary.
>So, while boundaries might regularly fall on right of way or centerlines 
>of roads and rivers, they are rarely fixed to those lines (which takes 
>away some of the future benefit of using a highway in an admin boundary 
>relation).

This confirms my understanding of how such boundaries are defined (usually 
in law with reference to a specific survey). It is the most compelling 
argument against the gluing of admin boundaries to anything else.


>Brett Lord-Castillo
>Information Systems Designer/GIS Programmer
>St. Louis County Police
>Office of Emergency Management
>14847 Ladue Bluffs Crossing Drive
>Chesterfield, MO 63017
>Office: 314-628-5400
>Fax: 314-628-5508
>Direct: 314-628-5407
>
>
>
>-----Original Message-----
>
>Date: Mon, 31 May 2010 16:02:15 -0400
>From: Richard Weait <richard at weait.com>
>Subject: Re: [Talk-us] Admin limits
>To: "talk-us at openstreetmap.org Openstreetmap"
>         <talk-us at openstreetmap.org>
>Message-ID:
>         <AANLkTinwgqk7knOEndqyIFJ6mJMitE1kQix77pa5hrkc at mail.gmail.com>
>Content-Type: text/plain; charset=ISO-8859-1
>
>On Mon, May 31, 2010 at 3:49 PM, Richard Welty <rwelty at averillpark.net> wrote:
> > On 5/31/10 11:06 AM, Nakor wrote:
> >> ? ? Hello,
> >>
> >> I just have a quick question on admin limits. I have seen various
> >> practices when they are overlapping another feature (road, river, ...)
> >> and I was wondering if there was a consensus on the way to do it as well
> >> as the pros and cons of each methods.
> >>
> >> * Two separate ways with separate nodes
> >> * Two separate ways with common nodes
> >> * One way holding both tags (e.g. highway=residentail and admin_level=8)
> >> * other?
> >>
> > most think it should be your first choice, two ways with separate nodes.
> > some argue for
> > choice 2 (generally GIS people who don't ?like duplicate nodes), and
> > some bots and other
> > tools push that way.
> >
> > i've not heard of anyone advocating choice 3. me, i stick with 1, if it
> > were ever decided
> > that 2 was the thing to do, it'd be possible to get there with a bot.
>
>You will also hear folks suggest tag the highway as it exists, then
>add the highway to a boundary relation for the admin_level.
>
>When applied correctly, this makes corrections to the road geometry
>simple, makes the boundary follow the corrected road without a hassle,
>and is an excellent use of a relation.  This is not an argument to put
>the boundary on the road if the boundary does not belong on the road.
>The same benefits would apply for a boundary that follows a river or
>other exiting feature.

--
Alan Mintz <Alan_Mintz+OSM at Earthlink.net>