I have a shapefile layer with >27,000 polygons. I want to dissolve these together to create a footprint layer. The Dissolve tool works fairly well, but it has filled in what should be rings in the new layer. (Same result in both QGIS 2.14 and 3.4). They are gaps in the original layer, surrounded by multiple polygons, (i.e. these are true spaces, not rings in a single polygon, and they should not be filled). Can anyone suggest a way to avoid this happening, please? Or a workaround to fix the layer now that the rings have been filled?
Starting layer;
Post Dissolve tool - with rings erroneously filled
Desired output overlaid on the first dissolved layer showing the filled rings.
Edit
I have now managed to get it to work, so perhaps it was a bug or an issue with my input layers? Would still like to know why it was happening to avoid a repeat in the future.
