[Tagging] Cleanup flood tagging

Lukas Sommer sommerluk at gmail.com
Sun Dec 28 19:42:16 UTC 2014

PS: About 57% of the key “flood_prone” is “flood_prone=yes”. About 42%
of the key “flood_prone” is “flood_prone=no”. About 80% of the
elements with the flood_prone key are in 15 km × 15 km area in
Lukas Sommer

2014-12-28 20:32 GMT+01:00 Lukas Sommer <sommerluk at gmail.com>:
> Hello.
> In OSM there seems to be concurrent 2 tagging systems for flood
> tagging. And each of them seems to be incomplete.
> Just to remember: There are several types of flood. I think the most
> common types are:
> – case 1: caused by heavy rainfall: “on flat or low-lying areas when
> the ground is saturated and water either cannot run off or cannot run
> off quickly enough to stop accumulating” (from Wikipedia article
> “flood”). Typically various times during one year – and quite common
> in some African countries during the rain season.
> – case 2: caused by overflow of water of a riverbed: not directly
> related to rainfall at this spot (rainfall can be hundrids of
> kilometers upstream, causing a river overflow hundrids of kilometers
> downstream). Typically maybe one per year or maybe each two or three
> years…
> In OSM we have flood_prone. The wiki descript fits most with “case 1”:
> “ this is mostly applicable to roads that go under water after heavy
> rains”; so combining it with highway=* on OSM ways (alternatively on
> nodes within a highway) would be the typical use case. We have
> currently 204 nodes and 10 582 ways.
> In OSM we have also hazard_type=flood. The wiki description fits
> mostly (but not exclusivly) with “case 2”. Tagging areas as
> independent OSM elements seems to be the typical use case (no
> combining with other objects). We have currently 1 node and 56 ways.
> hazard_type=flood comes from OpenHazardMap – but OpenHazardMap wiki
> page hasn’t been updated since one year. OpenHazardMap seems to focus
> on landslide (hazard_type=landslide has 3 169 comparing with only 57
> elements for hazard_type=flood).
> Questions:
> – Shouldn’t we deprecate one of these tagging? If so, which one?
> – Shouldn’t we introduce a possiblility to distinguish river
> overflowing floods and directly rainfall related floods?
> – Only supplementary tagging of highway=*? Or independent OSM elements
> (areas)? Or both? Probably both makes sense.
> Suggestions?
> Lukas Sommer

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