Logical diagrams show how traffic flows, not physical connections. They answer: "How does data get from A to B?"
A logical diagram includes subnets and VLANs, routing relationships, firewall placement and zones, interface IP addresses, and protocol information like OSPF areas or BGP AS numbers.
You use logical diagrams during troubleshooting. When users can't reach a server, the logical diagram shows every hop, VLAN, and firewall in the path.
Keep diagrams at different zoom levels: high-level for the entire network and detailed diagrams for individual segments.