Flow Maps in cartography can be defined as a mix of maps and Sankey diagrams, that show the movement of quantities from one location to another, such as the number of people travelling, the amount of goods being traded, or the number of packets in a network.
The width of the connections shows the quantity. Sometimes you flow maps with arrows to display the direction of the movement.
The most famous example of a flow map, is Minard’s map of Napoleon’s disastrous Russian campaign of 1812.
Tools & Codes - Flow Map
Reference - Flow Map
- Minard's Map of French Wine Exports for 1864 (Wikipedia)
- Minard's map of Napoleon's disastrous Russian campaign of 1812 (Wikipedia)