<div dir="ltr"><div>On Sun, 1 Sep 2019 at 05:24, Warin <<a href="mailto:61sundowner@gmail.com">61sundowner@gmail.com</a>> wrote:</div><div><br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">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?</div></blockquote><div><br></div><div>Better than nothing. If you feel adventurous, you could try mapping it as two, non-overlapping,</div><div>constituent areas of a multipolygon and see what happens.<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div bgcolor="#FFFFFF">
<p>I asked this question some time ago. I was told it was not
verifiable and therefore not for OSM. <br></p></div></blockquote><div><br></div><div>My opinion is that if there is signage/road markings it's verifiable and mappable. When we</div><div>map the speed limit of a road from signs the only actual, verifiable information we have is</div><div>the presence of the sign, but we assume the sign is true and infer the speed limit of the</div><div>road from it. Same thing here: sign says it's prone to floods so we infer the place is prone to</div><div>floods.</div><div><br></div><div>Where I differ from some is that I'd consider official documents also providing verifiability</div><div>provided their copyright permits it.</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">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?<br></blockquote>
</div><div class="gmail_quote"><br></div><div class="gmail_quote">Period is the multiplicative inverse of frequency: normalize the units, multiply them together</div><div class="gmail_quote">and the result should be 1. Neither is appropriate in this case. A once-in-100-year event</div><div class="gmail_quote">does not occur at 100 year intervals, it has a probability of 1% of occurring (technically,</div><div class="gmail_quote">being equalled or exceeded) in any given year. <a href="https://en.wikipedia.org/wiki/100-year_flood">https://en.wikipedia.org/wiki/100-year_flood</a></div><div class="gmail_quote">So we should be tagging a probability. Technically, exceedance probability</div><div class="gmail_quote">for floods.<br></div><div class="gmail_quote"><br></div><div class="gmail_quote">Taginfo shows floodplain_probability used 77 times. Is that sensible? It's a floodplain or it isn't.</div><div class="gmail_quote">Also flood_probability 4 times (better) and hazard:probability once. The flood_probability value</div><div class="gmail_quote"> in taginfo is "100y" rather than 1%. People who used floodplain_probability divide into those</div><div class="gmail_quote"> who expressed a large number like 100 (probably meaning years) and those who expressed</div><div class="gmail_quote"> a small number like 1 or 0.5 (probably a percentage). The only value for hazard:probability</div><div class="gmail_quote">is "low" (which I consider to be effectively meaningless).</div><div class="gmail_quote"><br></div><div class="gmail_quote">I dislike floodplain_probability because it IS a floodplain with a probability of being</div><div class="gmail_quote">flooded, not a probability of an area being classified as a floodplain. Also because</div><div class="gmail_quote"> it's been given both in terms of years and percentages (except it's impossible to be sure <br></div><div class="gmail_quote">because nobody has given units, so maybe the 100 means it's 100% likely to flood and</div><div class="gmail_quote"> the 0.5 means it is likely to flood every six months). It's a mess.</div><div class="gmail_quote"><br></div><div class="gmail_quote">I'm fairly happy with flood_probability. There's something nagging at the back of my</div><div class="gmail_quote">mind saying I ought to be unhappy with flood_probability, but it's not telling me why.</div><div class="gmail_quote"><br></div><div class="gmail_quote">I like hazard:probability, especially if we document that it should be tagged as a</div><div class="gmail_quote">percentage (and ignore or fix the sole value of "low"). Only problem with it is that</div><div class="gmail_quote">hazard=* is a proposal from 2007 that is supposedly still active, so we'd have</div><div class="gmail_quote">to do something about hazard=*. Then again there is hazard_prone=* and</div><div class="gmail_quote">hazard_type=* which seem to have appeared in the wiki without a proposal</div><div class="gmail_quote">and have a few thousand uses.</div><div class="gmail_quote"><br></div><div class="gmail_quote">-- <br></div><div class="gmail_quote">Paul</div><div class="gmail_quote"><br></div></div>