Hi Jeff (and welcome) Those are not "layers" but faces on the exact same plane therefore they cause a sort of "Z-fighting". In real world, everything has some thickness but SU faces have practically zero thickness therefore if you place two faces on top of each other (and they cannot merge because one is in a group like in your picture), SU cannot "decide" which one to display and does this. You should give some thickness to your faces (or intersect them and delete some part of the lower one). Are you making this model for Google Earth?