Network data structures for geographic information science (GISci) are methods for storing network data sets in a computer in order to support a range of network analysis procedures. Network data sets are among the most common in GISci and include transportation networks (e.g., road or railroads), utility networks (e.g., electricity, water, and cable networks), and commodity networks (e.g., oil and gas pipelines), among many others. Network data structures must store the edge and vertex features that populate these network data sets, the attributes of those features, and, most important, the topological relationships among the features. The choice of a network data structure can significantly influence one's ability to analyze the processes that take place across networks. This entry describes the mathematical basis for network data ...