Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm using OGR to perform a union using UnionCascaded. All my polygons have been created by GDAL polygonize which ensures that all polygons follow pixel edges and should therefore align nicely. But I get these strange flat polygons looking like lines:

Example of union result with strange flat polygons

They are positioned at locations where two polygons met before they where unioned.

Can you recognise this pattern and what lead to it?

share|improve this question
up vote 1 down vote accepted

Investigating this a bit further left me thinking it could be numerical errors. Using the zero-buffer trick worked, but ofcourse slowed my process down considerably.

share|improve this answer

Your Answer


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.