[talk-ph] areas of mangrove

[David Groom]

Eugene
Thanks  Its so hard to look thorough all the past postings on the list

Regards
David


On 01/05/2016 00:06, Eugene Alvin Villar wrote:
> Hi David,
>
> Mangroves and wetlands have been discussed here in 2009 and 2010 but 
> no definite convention or guidelines was agreed upon. Please see the 
> following two threads for the previous discussions:
>
> https://lists.openstreetmap.org/pipermail/talk-ph/2009-April/000695.html
> https://lists.openstreetmap.org/pipermail/talk-ph/2010-July/002398.html
>
> Based on agreed practice in OSM, the natural=coastline is defined to 
> be the high water line. So mangrove areas would be normally at the 
> seaward side of OSM's coastlines. But I think the answer is between 
> your approach 1 and 2. Mangroves can actually extend to the land-side 
> of the coastline as the ground there would still be saturated with sea 
> water even if the ground is not submerged at high tide. The problem 
> is, the high-water line will rarely be visible on satellite imagery. 
> So I think we just map using approach 2 when doing remote/armchair 
> mapping and then hope that these can be refined in the future using 
> actual field surveys.
>
> Regards,
> Eugene
>
>
> On Sat, Apr 30, 2016 at 10:14 AM, David Groom <reviews at pacific-rim.net 
> <mailto:reviews at pacific-rim.net>> wrote:
>
>     There are two different approaches used in mapping mangrove  areas
>     in OSM
>
>     1)  Treat the boundary of the mangrove and the openwater sea as
>     the coastline, and then map the area between that line and the
>     "dry" land as wetland.  This means that the wetland symbols are
>     rendered over the white colour of the land, and that at zoom
>     levels 12 and lower the mangrove areas simply get shown as white,
>     with the sea outside them.
>
>     2)  Treat the boundary of the mangrove and the "dry" land as the
>     coastline, and then map the area between that line and the
>     openwater sea as wetland.  This means that the wetland symbols are
>     rendered over the blue colour of the sea, and that at zoom levels
>     12 and lower the mangrove areas simply get shown as blue sea.
>
>     Early today I added some mangrove areas and followed approach 2
>     because the coastline had been accurately mapped along the
>     mangrove / dry land boundary, as so I simply added the mangrove
>     area outside this, as it seemed the existing mapper had cleary
>     thought the coastline should be at the dry land boundary.
>
>     However at http://www.openstreetmap.org/#map=14/9.7497/125.6105
>     both these approaches have been used.  Approach 1  has been used
>     for Lamagon Island, where the boundary of the mangrove area and
>     the sea is tagged as coastline.  But Approach 2 has been used for
>     the island immeditately south, where the boundary of the dry land
>     is tagged as coastline.
>
>     On further investigation I see at
>     http://www.openstreetmap.org/#map=14/9.7003/125.6415 that Approach
>     1 has been used.
>
>     Has this issue been discussued before within the Philippine OSM
>     community, with any recommended way of mapping mangrove areas
>     being decided upon?
>
>     Regards
>     David
>
>
>
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