[Talk-us] Re: Boundaries and verifiability (was Re: Retagging hamlets in the US)
On 2015-03-25 09:54, Bryce Nesbitt wrote: There are many defacto boundaries created by roads, hedges, powerlines, ridges or bodies of water. I argue the most appropriate boundary in OSM is indeed the defacto boundary. If people are using, paving, weeding and farming the boundary, that's the one we can map. The legal boundary is not something OSM can adjudicate. Finding that boundary is a complex process involving survey points, land descriptions, and often handwritten records stored in dark basements. It also hardy ever matters, at least to a mapper or map reader. That may be true when it comes to private property, but the de jure boundary of a given village, county, etc. matters to many members of the general public, all of whom could wind up reading our map. To the extent that a given place has a de facto boundary -- which I take to mean a boundary not *administered* by a government -- we shouldn't map it as an *administrative* boundary, and we should avoid mapping overly subjective data in fine detail anyways. I would imagine that administrative boundaries like city limits are a matter of public record. Granted, the public record isn't necessarily free or online, and the city may well store it in a dark basement. But where we can ascertain the legal definition of a city limit while respecting our copyright policies, we provide a valuable service by turning that prose into free geodata correlated with other features like roads. TIGER gets us most of the way there for city limits but not for a major city's political subdivisions. -- m...@nguyen.cincinnati.oh.us ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
[Talk-us] Re: Boundaries and verifiability (was Re: Retagging hamlets in the US)
On 2015-03-25 08:12, Martijn van Exel wrote: On Wed, Mar 25, 2015 at 3:00 AM, Minh Nguyen wrote: On 2015-03-24 13:57, Martijn van Exel wrote: 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. OK, thanks for clarifying. One risky use of administrative boundary data at the local level would be for tax purposes. Obviously we don't want people relying on OSM to decide whom to pay taxes to. That's why we have a disclaimer. [1] It should get more prominence. Wikipedia's legal and medical disclaimers are two hops away from every article, but ours is two hops from the wiki's main page only. At least consumer-focused redistributors of OSM data tend to have more accessible disclaimers. [1] http://wiki.osm.org/wiki/Disclaimer 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. I agree entirely, and I think OSM is already set up for these distinctions. If you see a boundary=administrative admin_level=10 relation on the map, you'd expect it to be an official (aka administrative) boundary, not a vernacular one. If you see a place=neighborhood POI with the name tag, you'd expect both definitions to be roughly equivalent. A purely vernacular neighborhood would be a POI probably tagged with loc_name instead of name. -- m...@nguyen.cincinnati.oh.us ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
[Talk-us] Re: Boundaries and verifiability (was Re: Retagging hamlets in the US)
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. -- m...@nguyen.cincinnati.oh.us ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
