[talk-ph] Automated assessment of OSM coastline data quality

Eugene Alvin Villar seav80 at gmail.com
Sat Apr 13 19:26:22 UTC 2013

Hi guys,

Here's a nice analysis done by Christoph Hormann in automated assessment of
the quality of OSM's coastline data:

If you don't want to read the whole article, here's the TL;DR version:

Coastlines where there are a few nodes per kilometer AND where the angle at
> each node is large means that the coastline is most likely to be of low
> quality. The last map image in the article highlights areas in the world
> where these "low" quality coastlines are located such as large parts of
> Indonesia.

The Philippines is on the "average" to "probably good" side of the scale. I
think this is thanks in a large part to the coastlines correction
collaboration the OSMPH community did 3 years ago:

But if you look at Japan, you can see that it is on the "probably very
good" side of the quality scale. So the Philippines still needs a lot of

If you want to help out improving the OSMPH coastlines, you can do the
1. Go to the OSMPH imagery coverage map (either
http://maning.github.io/Imagery_Coverage_Map/ or
http://tools.openstreetmap.org.ph/imagery_coverage/ )
2. Look for remote/provincial coastline areas with high-res Bing satellite
3. Zoom into a coastline, then switch between the Bing and OSM/MapQuest
background layers to check the coastline accuracy
4. Click on the "Edit in Potlatch" or "Edit in JOSM" link to edit away!
(You need to enable JOSM's Remote Control feature [it is enabled by default
in newer JOSM versions] for the "Edit in JOSM" link to work.)

If you're using JOSM, the Improve Way Accuracy tool (
http://josm.openstreetmap.de/wiki/Help/Action/ImproveWayAccuracy) is
*extremely* helpful. If will eliminate the need to click-drag your mouse.

Maybe in the future, we can recreate the quality algorithm developed by
Christoph Hormann and create a webmap specific for the Philippines. :-)

Keep on mapping!

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