[Tagging] How to tag flood prone points and areas?

Joseph Eisenberg joseph.eisenberg at gmail.com
Sat Aug 31 07:28:58 UTC 2019

It appears that most features with the tag "flood_prove=yes" are
covered by water on a somewhat frequent basis, perhaps once every year
or two, to once a month, or even more often during a rainy season.

However, I believe most of these features are prone to "flash
flooding", since they are often mapped in dry areas like Australia,
and the description says: "Whether or not the feature is likely to
flood after very heavy rain."

So this tag might be appropriate if the features that you want to tag
are somewhat frequently flooded, like at least once every year or two,
or more often.

If your survey data was more on the basis of "this feature has a 1% to
10% chance of flooding on an annual basis", that is, 10 year or 100
year flood risks, then I would use a different tag, not

But it's also questionable if entering 10 year or 100 year flood zones
(places that statistically have a 10% or 1% chance of flooding during
a 12 month period) into OSM is a good idea. The OSM database is based
on individual mappers, usually volunteers, entering data based on what
they can see when they visit a place, or what they can see on aerial
imagery. It would be difficult for individual mappers to confirm if a
10 or 100 year floodplain was entered incorrectly.

In contrast, it's easier for mappers to verify if a tag like
flood_prone=yes is correct on a highway if there are signs that say
"flash flood area" or "floodway" or similar, or if the area floods
after every heavy rain and this is common local knowledge.

Joseph Eisenberg

On 8/31/19, Graeme Fitzpatrick <graemefitz1 at gmail.com> wrote:
> On Sat, 31 Aug 2019 at 13:23, Immaculate Mwanja <
> immaculate.mwanja at hotosm.org> wrote:
>> After collecting all the information, we decided we should upload them in
>> OSM to be shared with the world since it was a successful project to some
>> extent. The challenge came when we could not upload these data since
>> there
>> is no specific tag to use for amenities or AoIs affected by floods, the
>> only tag that we could find is flood_prone=yes
>> <https://wiki.openstreetmap.org/wiki/Key:flood_prone> but this is mostly
>> applicable to “roads/ways" that go underwater after heavy rains.
> Had a read of the tag & while it does say roads & ways, I can't really see
> any reason why you couldn't use it for other POIs?
> Thanks
> Graeme

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