Flow maps

A flow map (or flow chart) combines a graph and a map to show the movement of goods, people or vehicles between places. It is also called a dynamic map.

To draw one you need:

• a route map showing the connections;
• flow data, with the origins and destinations;
• a scale for the width of the flow lines.

The width of each line is proportional to the amount moving along it. Example: at a scale of 1 cm = 40 buses, a route with 40 buses is drawn 10 mm wide, and a route with 10 buses 2.5 mm wide.

Add a terraced scale in the legend, and symbols for the places (stations, towns).

The book's examples show trains from Delhi, and the flow of water in the rivers of the Ganga basin. The width shows how much moves.