On Thu, Jan 10, 2019 at 4:47 PM Daniel Koć <daniel@koć.pl> wrote: > BTW: if we want to use proportion of length to area, we claim that we > know this area somehow.
If the feature is represented as a polygon, we do. If we have confidence that at least some shoreline is unambiguously part of the peninsula's shoreline, take the smallest shoreline in which we have confidence, strike an arbitrary line between its endpoints to complete a polygon, use that polygon to compute the area. Since this is a rough guideline, it doesn't need to be mathematically precise. Whether you estimate that the boundary of Cape Cod is the canal, or a line from approximately Wareham to Plymouth, or a line running approximately NE from Buttermilk Bay, you'll still find that the length of the land border is many times less than either the length of the waterfront or the square root of the area. Similarly, with Nova Scotia, the answer won't change whether you draw the border from Truro to Trenton or across the narrowest part of the Chignecto Isthmus, or at the provincial border. For almost any tag, in almost any situation, we defer to local mappers when we come close to the borders of "what sort of object is this?" I would not protest if a Michigander were to map the Upper and Lower Peninsulas, setting their boundaries as the state line, because that's the local understanding. If the Iberian Peninsula were to be mapped, I'd defer to the Europeans where to put the arbitrary land border. It seems that cutting across the narrowest part would be wrongheaded - it would exclude much of Catalonia, including Barcelona. But I'd let the mappers of Andorra decide whether the arbitrary line should include them. For the use cases I have in mind (using the shape of a partially-indefinite area to guide label shaping as well as placement), the precise arbitrary line will make no significant difference to the rendered result. The worst case will be that the terminal A in a curved IBERIA might be a little closer to Zaragoza or a little closer to Toulouse. If the 'G' in 'Gulf of Bothnia' (or the 'P' in 'Pohjanlahti) is a little bit closer to or farther from Åland, that will not matter a bit - the label will still render on a curved light, roughly south to north, from there to somewhere offshore of Oulu. But rendering it well does require information about the shape of the object. In short, there are effective uses to be made of the data, and effective guidelines that can be set for tagging them, even if there's less than perfect precision in the guidelines, or the shape depends on some indefinite boundary. To discard that information on the basis of 'verifiability' is 'all or nothing' thinking. Surely the Gulf of Finland verifiably exists. Surely Helsinki, Tallinn and Saint Petersburg are all verifiably on its shores. The fact that there is no precise line to separate it from the Baltic Sea should not prevent an application from being able to benefit from the incomplete information that is knowable about its shape. It's a delicate philosophical point, and it's one that we stumble over in this list regularly: when the existence of an object is verifiable, but there is only partial information known (or knowable, as in the case of virtually any waterbody or most area landforms) about its geometry or other attributes, is that object 'verifiable' for the purposes of OSM? We have decided that we can map rivers - despite there being an impossible-to-define line that separates the river from the lake or sea into which it empties. (And we haggle endlessly over the rules for drawing that line.) We've decided that mapping bays is mostly unacceptable - because of the arbitrariness of the mouth of the bay but in practice more because larger bays produce data that overwhelms databases and data consumers (hence the revert of the Gulf of Bothnia relation) - and similarly, we reject seas. We mostly accept political divisions with indefinite borders (but struggle over disputed ones). Now we struggle with peninsulas. The stated reasons are all the same - that a portion of the geometry is not verifiable, therefore even the verifiable part of the geometry must not be mapped. I'm no philosopher. I simply have a wish to render certain features based on the incomplete data that are knowable and verifiable. Some of the philosophers tell me that my understanding of the world is wrong - that such features aren't 'real'. I *think* I see them. _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging