I want to intersect contours with polygon like in the image below. But I got this error:
Warnings: GEOS geoprocessing error: One or more input features have invalid geometry. Some output geometries may be missing or invalid.
I don't know what's wrong with my geometries. I even don't know, where to search. I tested it also with a simple single-line. Same thing happened. The result: a empty shapefile
What should I do now? Where can I expect an invalid geometry? Or is it because of the shapefile (OGR ESRI)? Please help!