[talk-ph] areas of mangrove

[Eugene Alvin Villar]

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>
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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