Knowing how to convert a physical topology into a logical topology that suits your demand is the first thing you have to do for your network to get up and run. In practical most of the networks are connected like this:
As you can see, all the routers are connected to two switches Sw1 & Sw2. If the network is large enough, Sw1 & Sw2 should belong to Core layer which requires high speed switching because they have to do hardest work in the network. They should be powerful to mitigate congestion if occurs. Redundancy is also very important in this layer by providing multiple paths so that when a link goes down packets can still travel to the destination. Sw3 & Sw4 requires less power to proceed traffic and they should belong to Distribution layer. The last layer, which is not presented here is the Access Layer where switches are connected directly to the end users/terminals. In fact Sw3 and Sw4 can be used in Access Layer if the network is not large.