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 <[email protected]
<mailto:[email protected]>> 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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