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Combining coastlines for rendering

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?

rendering osm coastline

asked 05 Oct '11, 14:49

pastorgluk
31●1●1●4
accept rate: 0%

edited 05 Oct '11, 17:53

Jonas_
662●15●22●33

2 Answers:

I strongly recommend these wiki pages:
https://wiki.openstreetmap.org/wiki/Coastline
https://wiki.openstreetmap.org/wiki/Coastline_error_checker

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.

answered 05 Oct '11, 16:58

Pieren
9.8k●20●83●157
accept rate: 15%

edited 05 Oct '11, 16:59

1	One starting point can be here in the OSM wiki: Coastline answered 05 Oct '11, 16:56 stephan75 12.6k●5●56●210 accept rate: 6%