Many a time and oft I've spent hours struggling with bizarre bugs resulting from invalid geometries. The symptoms vary greatly, including:
- Database slowdowns
- Incorrect\Null query results
- Log files overloaded with errors and warnings
- Inconsistent result with geometric operators (e.g. intersection)
I would like to categorize the types of invalid geometries, in order to help everybody here sanitize their data.
Please answer with your favorite type of invalid geometry (one type per answer). Screenshots, descriptions and solutions are welcome - but try to keep your answer short.