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I'm writing simple rendering for OSM maps, and I have found that lands border is not one polygon but multiple coastline ways. So my question is how to combine them to one path for rendering? Is there some criteria for combining ways or it is done through relations?

asked 05 Oct '11, 14:49

pastorgluk's gravatar image

accept rate: 0%

edited 05 Oct '11, 17:53

Jonas_'s gravatar image


I strongly recommend these wiki pages:

It's explaining how coastline rendering works, why we need special tools to monitor them in OSM and the different type of errors we can find.
But two simple rules to remind : coastlines are not assembled with 'relations' and ways tagged with "natural=coastline" have the "water on the right". You may find many coastlines being part of relations but this is mostly for administrative boundaries, never for the coastline itself.
Saying that, the solution for you will depend on which zoom level(s) your simple renderer works. You might also have a look on how the application mkgmap (converting OSM data to Garmin GPS) is generating sea polygons.

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answered 05 Oct '11, 16:58

Pieren's gravatar image

accept rate: 15%

edited 05 Oct '11, 16:59

One starting point can be here in the OSM wiki:


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answered 05 Oct '11, 16:56

stephan75's gravatar image

accept rate: 6%

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question asked: 05 Oct '11, 14:49

question was seen: 6,926 times

last updated: 05 Oct '11, 17:53

NOTICE: is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum