Source: National Archives of Ireland.
Sankey diagrams visualize the magnitude of flow between nodes in a network. This diagram focuses on the flow of Irish immigration during the period 1845-1855: Points of departure are on the left, and destimations are on the right. Intermediate nodes group intermediate ports of transfer. The thickness of each link represents the number of individuals from source to target.
The fully automatic layout is convenient for rapid visualization—positioning nodes manually is tedious! However, the algorithm is not perfect; links are drawn with partial transparency to highlight crossings. To improve readability and further disambiguate links, this example also lets you reposition nodes interactively. The algorithm could be improved in the future, say to minimize link crossing or to support loopback in cyclical networks.