(I hadn't subscribed to this list, so the reply is to a seemingly random message and not directly related to that)
I believe much of this recent discussion is happening because there's a ... misconception that hasn't been addressed, and the actual tags that have been mentioned suggest readers to believe so. I believe I've mentioned this idea in the past, but I feel compelled to have it included in the discussion so that the arguments on either side refer to the same concepts. When a way no longer is an intact railway (or railbed), we don't want to claim it "is a railway" but rather "this was a railway"; the railwayness becomes an attribute of what is, i.e. "this row of trees and this embankment were for a railway and part of the railbed"), when previously it described "an object", i.e. "this is a railway and railbed". In short, they shouldn't use the same *key* in the tag. I therefore propose ** instead of changing the tag value to railway=dismantled, it would be better if mappers changed the tag key to "was:railway"="rail" following the method of lifecycle prefixes (quotation marks only for added readability) ** http://wiki.openstreetmap.org/wiki/Lifecycle_prefix The prefix can be dismantled: or razed: or destroyed: or removed: or was: or something else; I personally prefer "was:" as it's applicable to a lot of other cases, and applies to all that "were" something. At least that way the information (that the real world object no longer is an object) is stored in osm, in contrast to plain deleting which doesn't tell anyone if it was deleted because the way was a mapping mistake or just replaced by a better version. Even if it's deleted later by someone who finds it impeding his editing, it is still *possible* to extract that difference. With a change of key, even those who blindly draw all ways with railway=* (for example the humanitarian layer on osm.org seems to do so) won't be drawing false features. Reassembling straight-away-deleted railway ways and figuring out which ways presented the last coherent state of things requires manual work from everyone who wants to see that information (think 30 years from now), but if the real world removal is first tagged, the most manual part of that work is already done, even if somebody later deletes the ways. And it would be at least possible to automatically watch for and store all those objects in OHM or similar, but discard the "technical deletions". At least in urban environments the small details that tell a railway existed can remain for centuries: unusual colonnades, loading platforms, fasteners on the walls, curved buildings in an otherwise square road network etc., so the line between "totally gone" and identifiable isn't a clear cut line; why would it be paramount to delete stuff just when the iron beams were lifted, or when new asphalt was poured there? A possible life of a railway section in urban environment, a simple case: - the railway construction starts: railway=construction - the railway is in active use: railway=rail (say, in this example, in the middle of the city harbour, between warehouses which even have loading platforms at the height of the freight carriage floors) - the railway is no longer needed, no trains run there: railway=disused (everybody sees it's a railway). (a road had been built between the warehouses) - the track is converted to a sidewalk (the harbour is scaling down), but the loading platforms and the geometry remains; the way was a railway, and can be identified as such with expertice, and/or local knowledge and/or old sources: following the method of lifecycle prefixes, the best tag: "was:railway"="rail" The road under my window is a bus-only road, that was a freight rail track for decades (tracks ran in the center) before the buses started to run there, then only occasionally used at night, then disused for some years before the tracks were removed last summer. They'll build, eventually, tram tracks where the driving lanes are now, but then the road (emergency vehicles only) will still be something that was a railway track. A linear clearing with some scrubby young trees in a small but healthy wood area nearby is also there because that freight track was partially realigned a few decades ago (only the tracks were removed, still railway=abandoned). If nothing is built there, the line could, in some or several decades, become indistinguishable; at that point it would be appropriate to change to was:railway=rail. Verifiability doesn't mean it's easily seen with the naked eye at ground level, but that the next person can use any combination of observations, previously mapped related data, and reliable sources to make up their mind if the feature is or isn't (or wasn't) correct. That way drawing multiple generations of past buildings in cities with a long history (an example mentioned here) wouldn't be verifiable, because even if some preindustrial maps are suprisingly accurate, the sources don't have enough accuracy to tell how their location relates to the interim incarnations or to the present day data. As a counterexample, though, the city has built, in a park, a square sett surface at the location where the first town hall was up to 1640, based on their research. It's a highway=pedestrian, with a note tag explaining the historic significance, and was:building=townhall and end_date:building=~1640. If old documents told of another building with enough details to relate its location to the townhall, there shouldn't be no harm in marking that area likewise; it shouldn't matter if I were to pound some sticks in the grass at the corners to justify tagging those first, and then tagging "oh btw these also demarcate the site of ..." I believe rail data has become the main argument in these discussions, because the "better" maps became commonly available (very) roughly at the same time as the first railroads were being built and they leave much more partial traces than any or most other features. IMO even in a fully cleared new construction site, if on both sides of that area there are abandoned or in any way identifiable ends of a present or former railway, the was:railway=rail way through the new development won't hurt anyone; the ends combined with other sources verify it did go through the area. Only when the whole subnetwork of rails has been completely erased, it's fair to move the data elsewhere - before that, it relates to and tells something about the remaining parts or of their remains. Somebody suggested that storing historic administrative borders would be excessive or out of line; I say if anybody can deduce and map them, they deserve to be available and related to present day features. E.g. municipalities do merge and sometimes swap plots, and any research of history would benefit if the boundaries of former municipalities were available. We just wouldn't tag them as boundary=administrative, but was:boundary=administrative (with relevant date tags). Even old country borders aren't available, but historic documents may include description of their boundary stones (some still exist, historians have documented these) or geographic features used as the defining points. The sections between those points can be very, very long, so if they were commonly editable and publicly stored they would tell something about the current data: "this house is built in a location that was in country X up till year 1823, in Y between 1823 and 1917 and in country Z since that" - an attribute of the present day world just stored in the least complex way, i.e. in a similar way as the present day borders. The former border is still where it was. The borders don't usually have too many turning points, and they follow the same lines even for centuries, so these won't make editing more difficult, in any detectable amount. -- alv _______________________________________________ talk mailing list talk@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk