[Tagging] Coastal beach definition for mapping.

Warin 61sundowner at gmail.com
Wed Apr 4 01:00:13 UTC 2018

On 04/04/18 07:56, Warin wrote:
> On 03/04/18 18:32, Christoph Hormann wrote:
>> On Monday 02 April 2018, Warin wrote:
>>> The present OSM wiki defintion for beach
>>> is "Coastal beaches should be mapped down to the mean high water
>>> spring line (natural
>>> <https://wiki.openstreetmap.org/wiki/Key:natural>=coastline
>>> <https://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline>)"
>>> (from https://wiki.openstreetmap.org/wiki/Tag:natural=beach)
>>> I think this is incorrect .. they should be mapped past the high
>>> water mark to the low water mark.
>> This has been a disputed subject for a long time.  In any case the wiki
>> clearly does not reflect the current use of the tag here though.  The
>> following situations exist frequently in reality:
>> a) coast at high water line, beach only above high water line. This
>> leads to very narrow beaches since the area correctly to be tagged as a
>> beach is only between the regular high water line and the extreme
>> (storm flood) high water line.
>> b) coast at high water line, beach down to lower end of beach (either
>> the low water line or the transit of the beach to a tidal flat -
>> sometimes, in particular in the UK, the tidal flat is also incorrectly
>> tagged natural=beach).
>> c) coast at an intermediate water level (the level shown in whatever
>> image is used), beach ends at this water level (i.e. mappers directly
>> draw what they see in the image).
>> All variants are common, (a) in my experience is not more common than
>> (b).
>> For clarity regarding the difference between beaches and tidal flats:  A
>> beach is formed by waves, it therefore always has a significant slope
>> and is rarely wider than a few hundred meters.  A tidal flat is a flat
>> area exposed at low tide that is shaped by the tidal currents.
> Thanks Christoph, had not considered 'tidal flats'...
> there are some large areas I know of ...
> was thinking about them while I considered 'beaches', but had not 
> considered the term 'tidal flats'.

Humm tidal flats are sometimes called 'mud flats' ...
Came across this from the US Army https://definedterm.com/a/document/10633
tidal flats - (1) _Marsh <https://definedterm.com/a/definition/88100>_y 
or muddy areas covered and uncovered by the rise and fall of the _tide 
<https://definedterm.com/a/definition/88503>_. A TIDAL MARSH. (2) _Marsh 
<https://definedterm.com/a/definition/88100>_y or muddy areas of the 
seabed which are covered and uncovered by the rise and fall of tidal water.

beach - The zone of _unconsolidated 
<https://definedterm.com/a/definition/88535>_ material that extends 
landward from the _low water line 
<https://definedterm.com/a/definition/88065>_ to the place where there 
is marked change in material or physiographic form, or to the line of 
permanent vegetation (usually the effective limit of storm _wave 
<https://definedterm.com/a/definition/88560>_s). The seaward limit of a 
beach--unless otherwise specified--is the mean _low water line 
<https://definedterm.com/a/definition/88065>_. A beach includes 
_foreshore <https://definedterm.com/a/definition/87684>_ and _backshore 
<https://definedterm.com/a/definition/86032>_. (See Figure A-1) See also 

So a 'beach' may include a 'tidal flat' ... confused.

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