In general, a network is a system of interconnected linear features through which resources are transported or communication is achieved. The network data model is an abstract representation of the components and characteristics of real-world network systems. One major application of network analysis is found in transportation planning, where the issue might be to find paths corresponding to certain criteria, like finding the shortest or least cost path between two or more locations, or to find all locations within a given travel cost from a specified origin. This study will investigate the subject of network analysis in both raster and vector GIS, in order to compare the two spatial models. It will discuss their limitations and advantages, by using a road network as an example.
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.