The node and the link, the building blocks of connectivity.
“Data visualization models that are intended to depict considerable sets of interrelated data (including systems designed to process and render big data, particularly those that must reveal unexpected correlations) and data- supported massive-communication toolsets (such as social-network media systems) increasingly rely on presentations that depict relationships through node-and-link diagrams. The challenge of combining these kinds of quantitative and qualitative datasets can be well met with node-and-link diagramming — provided an articulate and consistent modelling method is applied to the task. This paper is a primer on what node-and-link diagrams are, and what kinds naming categories may be derived and assigned in order to make node-and-link diagrams articulate and consistent.”
(William M. Bevington ~ Parsons Journal of Information Mapping Spring 2015)