Final answer:
In network flow problems, decision variables, which determine the flow from one point to another, are represented as arrows in the graphical network.
Step-by-step explanation:
Decision variables in network flow problems are represented by arrows in the graphical network. These arrows indicate the direction and quantity of flow from one node to another. In network diagrams, nodes, which are points where lines intersect, are often represented as circles or other shapes, but the actual movement or flow of resources, data, or whatever is being analyzed in the network is depicted with arrows. For instance, in transportation problems, arrows illustrate the number of goods moving from an origin to a destination.