I am working with elevation curves and I want to group curves by elevation. I can do it with the Split Vector Layer tool (Vector, Data management Tools) and choose ELEV as a unique ID field.

However, if first I Simplify the curve (Vector, Geometry Tools) and then Split, the resulting layers are invisible. I still have a layer for each elevation, and each has a different colour tag assigned. I can even Zoom to layer and it zooms where the elevation curve is supposed to be, but nothing is shown. Attribute table shows that the layer is not empty, and I can create a polygon with Lines to Polygon, however also the polygon is invisible and zoomable. When I use the polygon to clip another polygon, I get the error

"Feature (525) from “Polygons” has invalid geometry. Please fix the geometry or change the “Invalid >features filtering" option for this input or globally in Processing settings.

I could first split all elevation lines and then simplify each, but it is a much longer process.

What am I doing wrong? Cheers

I am working with elevation curves and I want to group curves by elevation. I can do it with the Split Vector Layer tool (Vector, Data management Tools) and choose ELEV as a unique ID field.

However, if first I Simplify the curve (Vector, Geometry Tools) and then Split, the resulting layers are invisible. I still have a layer for each elevation, and each has a different colour tag assigned. I can even Zoom to layer and it zooms where the elevation curve is supposed to be, but nothing is shown. Attribute table shows that the layer is not empty, and I can create a polygon with Lines to Polygon, however also the polygon is invisible and zoomable. When I use the polygon to clip another polygon, I get the error

"Feature (525) from “Polygons” has invalid geometry. Please fix the geometry or change the “Invalid >features filtering" option for this input or globally in Processing settings.

I could first split all elevation lines and then simplify each, but it is a much longer process.

What am I doing wrong?