Links represent a physical entity or process within the system, but one that incorporates transportation from an upstream node to a downstream node. Stormwater pipes, channels and sewer mains are all examples of entities represented by links.
Links are used to connect nodes.
The Urban Developer Plugin currently does not support routing of flows. Inflows are directly translated to outflows, ie links do not store or route water.
You can only connect nodes using links. You cannot connect two links to each other without an intervening node.
Urban Developer attempts to simplify the model setup process and prevents conceptual mistakes such as connecting a node input to a node input, or an output to an output. There are restrictions on which node inputs and outputs you can connect together. See Node Connection Rules.