[Tagging] tagging floodplain

Christoph Hormann chris_hormann at gmx.de
Sun Sep 25 20:37:23 UTC 2016

On Sunday 25 September 2016, Warin wrote:
> [...]
> So .. what would be the best key to use for this feature/value?

In general the problem about tagging flood risk is verifiability.  How 
often should an area be subject to flooding to warrant such a tag?  In 
case of flood events that occur maybe once every 5-10 years this is 
hardly mappable in OSM in most cases.

If you are talking about areas that are dry most of the time and flooded 
only occasionally or for short periods it would be best to map this as 
whatever it is in a dry state and tag the occasional flooding as a 
supplemental tag like flood_prone=yes.

Note the term 'floodplain' does not necessarily refer to areas that are 
water covered as a whole at any time.  The plain of a braided river for 
example is often simply the area the river rapidly changes its course 
in.  This should probably not be tagged the same way as an area 
frequently water covered after heavy rain.

Christoph Hormann

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