Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

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

share|improve this question
    
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
add comment

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.

share|improve this answer
    
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
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.