I always did press Q, it just didn't always square them completely. Any time I added a layer, it was as the existing mapping appeared wrong and I wanted to map something in it's place, but didn't want to disregard someone else's work and assume I knew better than them. I never edited any roads, only buildings, and if anything asked me to resolve something being on top of something else, I always clicked the option to put it on the layer below. 