I'm a QGIS beginner. I have twenty layers of drive time polygons. There are multiple overlapping polygons between the layers. All attribute tables have identical field names. I can merge these multiple layers without issue, using any of the available tools in QGIS. I have not found a way to retain the minimum drive time for each merged polygon. All of the tools seem to sum by default. Although I have not yet had success rasterizing these layers, my guess is that I can do these calculations with rasters. However, I was hoping there might be a way to do this while keeping everything in vectors. Any ideas?
Example of overlapping polygons between layers:
Layer 1 - Drive time = 160s
Layer 2 - Drive time = 100s
Layer 3 = Drive time = 135s
I want the new merged polygon to have a value of 100s.
The answer below worked for me but I needed to use the "contains" option, not "intersect" to get the exact results I wanted. Also, I got odd looking layers from my first experiments, with many polygons receiving no values. I traced this problem to invalid polygons, which I corrected with the v.clean function.