This question on Multilayer intersection in QGIS was asked by "julsbreakdown" a year go. But I am a newbie and I am not really sure how it works with SQL as suggested in the responses. And I am using the same image posted by "julsbreakdown." Here is the link of the previous thread: Multiple layer intersection
Using QGIS (or its plug-in) or python script, how do I get the polygon (x) which is the intersection of four polygons?