Nodes can be junctions and edges can be segments of a road or a pipeline. For a network to function as a real-world model, an edge will have to be associated with a direction and with a measure of impedance, determining the resistance or travel cost along the network. Click to enlarge Typical network graph and table structure, listing nodes, connectivity of edges, turn impedance and edge attribute data. Since networks utilize the basic arc-node structure, by definition, due to the way the data is stored, the vector network will already have a topological structure, relating all elements. All that is needed, simply speaking, is to implement the resistance factors in the attribute tables for the lines or nodes.
Directions are an explicit part of the vector network topology.
If the directions are derived from digitising a road map, or received as a ready coded network form a data supplier, they may not correspond with the real-world directions and need to be checked. Consequently, the representation of network elements requires substantial amount of time to be devoted to data preparation and validation. Arcs usually describe the centreline of a network feature, such as a road centreline. Arcs and nodes are discretely referenced by coordinates. Also lines that cross, but not intersect, can be directly implemented in the vector model, much like in the real world, where we have overpasses and underpasses .