[Tagging] tagging floodplain

Colin Smale colin.smale at xs4all.nl
Mon Sep 26 00:00:11 UTC 2016

On 2016-09-26 01:18, Warin wrote:

> On 26-Sep-16 08:58 AM, Colin Smale wrote: 
>> On 2016-09-26 00:17, Warin wrote:
> Perhaps you could state your definition?
> One definition I saw briefly said something about the maximum expected area ... I only skimmed it .. looking for a open source map of the floodplain (by whatever definition :) ). 
> There are some 'floodplains' on the NSW LPI Base Map - available in OSM (similar availability to Bing imagery - but has addresses, parks, forests etc). 
> The flood level in Forbes was supposed to peak at 10.7 metres .. over the 'normal' level of the river? Or over the bed of the river? I don't know .. but 10.7 is fairly high!

I don't have my own definition, and I don't want to make up a new one. A
quick search revealed these: 

 	* a nearly flat plain along the course of a stream or river that is
naturally subject to flooding.
 	* an area of low, flat land along a stream or river that may flood
 	* an area of land built up from soil left by floods
 	* level land that may be submerged by floodwaters [1]
 	* a plain built up by stream deposition

They all sound rather open to interpretation, but they are all based on
natural phenomena, not government classifications. 

> I would expect this to be similar to other OSM 'definitions' like stream vs river, monument vs memorial, city vs town vs village .. a bit fuzzy to allow for local variations. 
> For example in India the definitions of places looks to be swinging to the legal/government determined rather than simply population based.

This is also frequently the case in the UK by the way. 

The distinction between city and town, and between river and stream, is
cosmetic, and the fuzziness doesn't hurt. The fuzziness is in whether
something is "big" or "small" and there will always be debates about
"medium" things. The fuzziness in these examples does not affect where
the lines are drawn on the map, only the tagging. I don't see how that
principle would be applied to flood plains where the location of the
line itself is debatable. 


[1] http://www.merriam-webster.com/dictionary/floodwaters
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