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I am reducing the size of a world timezone shapefile,


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

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beta, but worth a try kelsocartography.com/downloads/gis/2012/natural_earth/… –  underdark Jun 16 '12 at 18:40
Shafefile is hard to reuse and is missing timezones, good start though –  Paul Salber Jun 16 '12 at 19:14
Can anybody recommend alternate tool to simplify geometry and reduce size of shapefile? –  Paul Salber Jun 17 '12 at 9:55
Check related questions such as gis.stackexchange.com/questions/178/… & gis.stackexchange.com/questions/3739/…. If you cannot find an answer that works in your case, please open a new question. –  underdark Jun 17 '12 at 10:35

1 Answer 1

up vote 4 down vote accepted

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.

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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
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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