Hi all, flood_prone=yes doesn't sound to be good semantics. Should we rewrite it as floodable=* with 3 or four big level of probability (or causes, or whatever) instead?
Many people raised concerns about yes/no tags and the key name seem to contain two distinct information (floodable + probability) while the value meaning could be improved. Furthermore, such work can be useful for many hazard description. This proposal is interesting : https://wiki.openstreetmap.org/wiki/Proposed_features/hazard Floods can also occur on river banks surroundings when hydropower is in operation upstream https://lists.openstreetmap.org/pipermail/tagging/2018-July/037973.html Here is what is often displayed : https://imgur.com/a/TLhZcgE All the best François Le dim. 1 sept. 2019 à 14:07, Joseph Eisenberg <joseph.eisenb...@gmail.com> a écrit : > For `flood_probability` to be useful and verifiable in some way, there > should be a link to the source in the changeset, or perhaps also > source: flood_probability= on the object. > > Such statistical features like "1% risk of flood per year" can't > really be verified by individual mappers, since they are based on > calculations of the floodplain geometry and historical observations of > floods over many decades. So it's probably more useful to have these > mapped in official sources which are kept up-to-date, rather than > importing the data from the external source into OSM, and then having > to maintain it in our database. > > I agree that if there is a sign that says "this area prone to > flooding", then "flood_prone=yes" is verifiable and helpful to add, > since that's representing a feature that can be checked when the area > is next survey. > > On 9/1/19, Paul Allen <pla16...@gmail.com> wrote: > > On Sun, 1 Sep 2019 at 05:24, Warin <61sundow...@gmail.com> wrote: > > > > You could add flood_prone=yes to the car park tag but that will show the > >> whole car park as affected, whereas it's only the bit down this end that > >> has a problem. Would drawing a separate area & marking that as > >> flood_prone=yes work? > >> > > > > Better than nothing. If you feel adventurous, you could try mapping it > as > > two, non-overlapping, > > constituent areas of a multipolygon and see what happens. > > > >> I asked this question some time ago. I was told it was not verifiable > and > >> therefore not for OSM. > >> > > > > My opinion is that if there is signage/road markings it's verifiable and > > mappable. When we > > map the speed limit of a road from signs the only actual, verifiable > > information we have is > > the presence of the sign, but we assume the sign is true and infer the > > speed limit of the > > road from it. Same thing here: sign says it's prone to floods so we > infer > > the place is prone to > > floods. > > > > Where I differ from some is that I'd consider official documents also > > providing verifiability > > provided their copyright permits it. > > > > However there is the question of frequency, once in 10 year event, once > in > >> 100 etc. So I would add a sub tag or value about frequency of the > event.. > >> The key frequency is already in use. Period has some use too, though the > >> use looks to be years.. no wiki to say what it is? > >> > > > > Period is the multiplicative inverse of frequency: normalize the units, > > multiply them together > > and the result should be 1. Neither is appropriate in this case. A > > once-in-100-year event > > does not occur at 100 year intervals, it has a probability of 1% of > > occurring (technically, > > being equalled or exceeded) in any given year. > > https://en.wikipedia.org/wiki/100-year_flood > > So we should be tagging a probability. Technically, exceedance > probability > > for floods. > > > > Taginfo shows floodplain_probability used 77 times. Is that sensible? > > It's a floodplain or it isn't. > > Also flood_probability 4 times (better) and hazard:probability once. The > > flood_probability value > > in taginfo is "100y" rather than 1%. People who used > > floodplain_probability divide into those > > who expressed a large number like 100 (probably meaning years) and those > > who expressed > > a small number like 1 or 0.5 (probably a percentage). The only value for > > hazard:probability > > is "low" (which I consider to be effectively meaningless). > > > > I dislike floodplain_probability because it IS a floodplain with a > > probability of being > > flooded, not a probability of an area being classified as a floodplain. > > Also because > > it's been given both in terms of years and percentages (except it's > > impossible to be sure > > because nobody has given units, so maybe the 100 means it's 100% likely > to > > flood and > > the 0.5 means it is likely to flood every six months). It's a mess. > > > > I'm fairly happy with flood_probability. There's something nagging at > the > > back of my > > mind saying I ought to be unhappy with flood_probability, but it's not > > telling me why. > > > > I like hazard:probability, especially if we document that it should be > > tagged as a > > percentage (and ignore or fix the sole value of "low"). Only problem > with > > it is that > > hazard=* is a proposal from 2007 that is supposedly still active, so we'd > > have > > to do something about hazard=*. Then again there is hazard_prone=* and > > hazard_type=* which seem to have appeared in the wiki without a proposal > > and have a few thousand uses. > > > > -- > > Paul > > > > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging >
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