[Talk-us] Boundaries and verifiability (was Re: Retagging hamlets in the US)

[Martijn van Exel]

On Wed, Mar 25, 2015 at 3:00 AM, Minh Nguyen <minh at nguyen.cincinnati.oh.us>
wrote:

> On 2015-03-24 13:57, Martijn van Exel wrote:
>
>> I have long been on the fence about boundaries in OSM, and while I don't
>> feel as strongly about it any longer, it still feels wrong to make this
>> sweeping exception to one of the fundamental conventions of OSM mapping:
>> verifiability. For many types of land use, anyone would be able to
>> verify boundaries on the ground: a forest, a corn field, even a retail
>> zone in most cases. But administrative boundaries can only be observed
>> in a limited number of places: wherever there is a sign or a physical
>> boundary in place, and rare other cases.
>>
>
> Admittedly, a given border can be observable along one segment but not
> another. However, we tend to map the entire border for the sake of
> completeness, convention, and technical reasons -- closed areas are much
> more useful than stray lines. OSM has long gone to extremes on this point,
> going so far as to enclose all continents and island nations in maritime
> borders.
>
> Hopefully you had the chance to read my case study on Illinois, Indiana,
> Ohio, Kentucky, and West Virginia earlier in this thread. [1] You can
> observe much of the Ohio-Indiana state line quite precisely, both on the
> ground via welcome signs and mile markers and from the air via changes in
> land use and pavement quality. But you cannot observe the Ohio-Kentucky
> state line except by visiting a library, and the Ohio-Ontario border is an
> imaginary line. Which of the five options would you have chosen for Ohio?
>
> [1] https://lists.openstreetmap.org/pipermail/talk-us/2015-
> March/014485.html


I have, and my (admittedly much more limited) experience in Utah does not
suggest I would be able to determine a reliable state boundary from
information on the ground. County lines even much less so.

>
>
>  More importantly though, there is an authoritative source for
>> official administrative boundaries that can be easily accessed by
>> anyone: TIGER[1]
>>
>
> You mean the way TIGER is an authoritative source for road centerlines?
> TIGER's boundaries vary in quality just as its roads and railroads do. I've
> taken quite a few imported municipal boundaries, lined them up with road
> easements or hedges between farms _when that is obviously the intent_, and
> deleted extra nodes. These borders become far more accurate and precise in
> OSM than in commercial maps, which regurgitate TIGER boundaries verbatim.
>

> The most authoritative source for most U.S. land borders, going all the
> way down to the parcel level, is a legal prose definition in conjunction
> with any number of monuments on the ground. Both metes and bounds and the
> Public Land Survey System rely on monumentation. A monument may be a major
> road or as obscure as a small iron pin embedded in that road, but even that
> pin is verifiable if not particularly armchair-mappable.


> If you're lucky, you can find an Ohio city limit's legal definition in
> county commissioners' minutes when an annexation is proposed. The most
> authoritative data representation is the county GIS database, which anyone
> can easily access -- for a fee. After paying the county for that database,
> you might well forget about OSM, because it's also the authoritative source
> for road centerlines and names.


That is actually not what I meant, but I could have been more precise. I
guess this turns into a discussion of what 'authoritative' actually means.
This is different things to different people. As OSM becomes better,
increasingly folks will start looking at us for authoritativeness, which
would make sense because everything is (supposed to be) verified on the
ground. Because administrative boundaries have legal implications, the
authoritative source will need to be someplace outside of OSM. It may
actually hurt OSM down the line if we include information that suggests
authoritativeness we cannot provide.


>
>
>  All of this has little to do with neighborhoods, which are mostly (?)
>> vernacular in naming and delineation, and even when there are official
>> neighborhood designations, in my own experience they do not always match
>> the vernacular names. I support point mapping of vernacular
>> neighborhoods. If you really want to have shapes for vernacular
>> neighborhoods, you can look at the now-ancient-but-still-cool flickr
>> Alpha Shapes[2], last updated in 2011 but still available for
>> download[3]. But please don't upload 'em to OSM :)
>>
>
> As a political boundary (in the political map sense), an official
> neighborhood designation can be distinct from the neighborhood with a
> vernacular name, but that's an argument to map both rather than favoring
> one over the other. They coexist and might share a name but aren't
> necessarily the same thing. People should be able to get the concrete,
> objective boundary of an official neighborhood from OSM and an amorphous,
> subjective boundary of an informal neighborhood from Alpha Shapes.


Sure, but vernacular and official neighborhood objects would then need to
be represented differently so folks can tell them apart and know what they
are dealing with.

Martijn
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