Flow map
Thematic map using linear symbols to show movement between locations.
A flow map is a type of thematic map that uses linear symbols to represent movement between locations, such as people, highway traffic, trade goods, water, ideas, or telecommunications data. It may be considered a hybrid of a map and a flow diagram, and its design varies widely depending on the moving material and geographic networks involved.
- field
- Cartography
- known_for
- Visualizing movement and flow volume using proportional line width
- key_figure
- Charles Joseph Minard (1850s–1860s)
Lore & Background
During the 1850s and 1860s, Charles Joseph Minard mastered the technique, producing forty-two flow maps on a wide variety of topics among his cartes figuratives.
Reader's Guide
Flow maps are significant for their ability to convey complex movement data—origin, destination, route, type, amount, direction, and velocity—in a single visual representation. According to Eduard Imhof, a flow map may represent several aspects of moving phenomena and the networks along which they travel. Types include origin-destination maps, distribution maps, network route maps, and continuous/mass flow maps. The most common technique to visualize amount or speed is through line weight proportional to value, similar to scaling methods for proportional symbol maps. During the 1980s, Waldo Tobler conducted experiments to create flow maps by computer, and while early results were not up to Minard's standards, subsequent improvements in GIS and graphics software have enhanced automated design capabilities. Flow maps remain essential in human geography (migration, trade, traffic) and physical geography (streamflow, wind, wildlife migration).
Did You Know?
- Charles Joseph Minard produced forty-two flow maps during the 1850s and 1860s.
- Waldo Tobler conducted experiments to create flow maps by computer during the 1980s.
Frequently Asked Questions
What is a flow map in cartography?
A flow map is a thematic map that depicts movement between geographic locations using linear symbols, where the width of each line is proportional to the volume being transported. It functions as a hybrid between a conventional map and a flow diagram, with its visual design shifting based on the type of material and the network involved.
Why is Charles Joseph Minard considered a key figure in flow-map history?
Minard, active in the 1850s and 1860s, elevated the flow map from a simple trade illustration to a powerful analytical tool for visualizing complex movements such as military campaigns and commodity flows. His work demonstrated that proportional line width could encode both direction and magnitude simultaneously, a principle that remains central to the technique.
What kinds of movement can a flow map represent?
Flow maps are not limited to a single subject; they can chart the movement of people, highway traffic, trade goods, water, ideas, and telecommunications data. The specific network and material being tracked determine how the linear symbols are styled and scaled.
How does a flow map differ from a standard choropleth or dot-density thematic map?
Where choropleth and dot-density maps emphasize static quantities tied to regions, a flow map encodes dynamic transfer between locations using directional lines. The proportional width of each line conveys volume, and the overall layout reads more like a diagram of connections than a shaded area map.
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