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

[Minh Nguyen]

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

> 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.

> 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.

-- 
minh at nguyen.cincinnati.oh.us