I'm currently reading an electromagnetism text book and it has said that Gauss's theorem can only be applied on: Concentric spheres Concentric cylinders Parallel planes In these cases the "symmetry allows the integrals to be evaluated" In class we only ever really use co-axle cables, micro-strip lines, parallel plates, and point charges as examples, as these all can be described by one of these 3 shapes. My question is asking about the more obscure shapes that could still technically be called one of these 3 shapes. For example when talking about micro-strip or parallel plates the planes are always above and below each other, as shown in the picture bellow. But can the two planes be next to each other? They would still be parallel, they are just now at the same height. For example a micro-strip with the feed and ground line both on the same side of the PCB.