I have also been doing "coastal cleanup" lately. Main reason being that since I use OSM map tiles for <a href="http://waypoints.ph">waypoints.ph</a> and since a lot of our destination waypoints are near the coasline (beaches and island destinations are the most popular), I wanted to have good coastline detail on OSM and correct those current "sawtooth" coasts.<br>
<br>Most interesting to clean up is the area around west Batangas, especially north Nasugbu which have dozens of mini peninsulas and promontories. They are interesting to look at now (on Osmarender for now as Mapnik may still take time to update the coasts) <br>
<br><a href="http://openstreetmap.com/?lat=14.1316&lon=120.6185&zoom=13&layers=0B00FTF">http://openstreetmap.com/?lat=14.1316&lon=120.6185&zoom=13&layers=0B00FTF</a><br><br>I did encounter similar concerns as Maning had too regarding mangroves and wide rivers. I am more particularly concerned if the landsat is actually accurate enough for mapping smaller details such as rivers ... similar problem with Yahoo imagery on Makati as reported earlier on another discussion. <br>
<br>Just recently, we took tracks and points on the Mangrove Project of Sariaya. We particularly and specifically navigated the wide river that divides the mangrove area and the tracks were taken with a GPS276C with external antena on the boat and had more than 8 satellites in view (very low position error). Now, when the tracks were superimposed on JOSM against the WMS landsat image, the river was off by as muchg as 50 meters! I just went ahead and used the GPS tracks instead of the landsat image for plotting the river:<br>
<br><a href="http://openstreetmap.org/?lat=13.82952&lon=121.46565&zoom=15&layers=B000FTF">http://openstreetmap.org/?lat=13.82952&lon=121.46565&zoom=15&layers=B000FTF</a><br><br>As what really to follow as "coastline", my opinion is to make existing structures or natural "protrusions" as the coastline. Not knowing what to really follow earlier, I looked at what was done to represent the coastline on the Manila Bay and Malabon area and I see that the coastline was traced along the piers and man-made "land" areas. So, I guess that will do well for showing piers / wharfs / mangroves /very wide beaches / tidal lands. <br>
<br>:>) ed<br><br><br><div class="gmail_quote">On Fri, Apr 10, 2009 at 11:46 AM, Maning Sambale <span dir="ltr"><<a href="mailto:emmanuel.sambale@gmail.com">emmanuel.sambale@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi,<br>
<br>
Since my etrex GPS died, I have resorted to coastline mapping to<br>
improve previous coastline import. I have completed several islands<br>
already and my next target is Luzon mainland (already completed most of<br>
north-east Luzon up to Ilocos Sur). At first, I thought it should be<br>
easy, just load LANDSAT WMS and your good to go. But really it isn't.<br>
<br>
Because,<br>
<br>
1) coastline is a fractal problem [1], at varying zoom-levels you get<br>
different details. Using landsat, you need to be at zoom 14-16 to get<br>
the most detail.<br>
<br>
2) I find it difficult to select, move, and delete nodes of the SRTM<br>
generated coastline. You have to use several keystrokes and<br>
mouse-clicks. What I do instead is delete several coastline ways and<br>
then create a new coastline way.<br>
<br>
Some questions:<br>
<br>
1) How do we map mangrove [2] areas along coastlines? In the "field"<br>
mangroves are either inland extending to the coast and even beyond<br>
coastline. Do we include mangroves in inter-tidal areas as part of the<br>
coastline?<br>
<br>
2) Where do coastline and large rivers converge? River deltas [3] is<br>
particularly problematic.<br>
<br>
3) Sand bars? Siltation areas? Any suggestions on how we map this?<br>
<br>
Me thinks: coastlines will never be complete because we have so much<br>
coastline and the threat of sea-level rise due to climate change<br>
<br>
<br>
<br>
<br>
[1] <a href="http://library.thinkquest.org/26242/full/ap/ap4.html" target="_blank">http://library.thinkquest.org/26242/full/ap/ap4.html</a><br>
[2] <a href="http://en.wikipedia.org/wiki/Mangroves" target="_blank">http://en.wikipedia.org/wiki/Mangroves</a><br>
[3] <a href="http://en.wikipedia.org/wiki/River_delta" target="_blank">http://en.wikipedia.org/wiki/River_delta</a><br>
<br>
--<br>
cheers,<br>
maning<br>
------------------------------------------------------<br>
"Freedom is still the most radical idea of all" -N.Branden<br>
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</blockquote></div><br><br clear="all"><br>-- <br>website administrator: <br>- <a href="http://www.waypoints.ph">www.waypoints.ph</a><br>- <a href="http://reeflife.eppgarcia.com">reeflife.eppgarcia.com</a><br><br>PADI Divemaster #491048<br>