I have a global DEM and try to calculate contour polygons for 4 different heights in QGIS. In the first image below, you can see the colored DEM (white = lowest; yellow = higher; orange = highest) as well as the overlying contour lines. The white area inside the yellow area is a sink.
After this i did convert the contour lines into polygons with the "Lines to polygons" function. Unfortunately, the sinks are not cut out in the polygon and remain the same class like the surrounding as you can see in the image below. The white areas from above have now the same class as the yellow area (its all pink).
Can someone explain me how I can archive, that the white area would have another class after polygonizing?