6

I am reducing the size of a world timezone shapefile,

http://efele.net/maps/tz/world/tz_world_mp.zip

But at a 0.01 tolerance, entire countries disappear

Anybody know a way round this?

QGIS shows the same error simplifying naturalearthdatamaps also; simplify with 0.01 tolerance and Italy disappears

4

Looks like a known problem http://hub.qgis.org/issues/4189

The reason for wrong behavior is a tiny ring. If it is removed, the polygon is simplified ok. The polygons with bigger rings simplify ok, but if any polygon has a ring that is smaller than tolerance, it breaks the whole polygon.

  • Ah, thanks. Well found. Looks like I need to ogr2ogr until the fix the bug in QGIS – Paul Salber Jun 16 '12 at 21:55
  • I have tried GRASS and openjump on the timezone shapefile. The first simplifies but does not reduce filesize, the second crashes on an error. In order to progress, I am happy to contract help, anybody interested? – Paul Salber Jun 18 '12 at 9:36
  • 3
    mapshaper.com/test/MapShaper.swf simplifies shapefiles, and is robust to ocurrence of polygon rings smaller than the simplify tolerance. – Paul Salber Jul 1 '12 at 16:41

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