Flow map
Thematic map using linear symbols to show movement between locations.
Unknown author · Public domain
A flow map is a type of thematic map that uses linear symbols to represent movement between locations, functioning as a hybrid of a map and a flow diagram. It can depict the movement of people, highway traffic, trade goods, water, ideas, telecommunications data, and other phenomena. The wide variety of moving material and geographic networks has led to many design strategies, with some cartographers expanding the term to any thematic map of a linear network, while others restrict it to maps that specifically show movement.
- key_innovator
- Charles Joseph Minard (1840s–1870s)
Lore & Background
In subsequent years, others experimented with the technique in Europe until it was mastered by Charles Joseph Minard.
Reader's Guide
Flow maps are significant because they provide a visual method for understanding the movement of diverse phenomena across geographic space, combining spatial location with quantitative flow data. The development of computer-generated flow maps began in the 1980s with Waldo Tobler, though early results did not meet Minard's standards; subsequent improvements in GIS and graphics software have enhanced automated design capabilities. Flow maps can represent multiple aspects of movement simultaneously, including origin and destination, route, type of movement, amount, direction, and velocity. Different design strategies have emerged for specific purposes: origin-destination maps focus on connections between places, distribution maps balance nodes and routes, network route maps emphasize the network itself, and continuous or mass flow maps visualize vector fields such as ocean currents or wind. The most common technique for showing amount or speed is line weight scaling, similar to proportional symbol maps.
Did You Know?
- Waldo Tobler conducted experiments to create flow maps by computer during the 1970s.
Gallery
Frequently Asked Questions
What is a flow map in cartography?
A flow map is a thematic map that uses linear symbols—such as arrows or lines—to visualize movement between two or more locations. It essentially blends a geographic map with a flow diagram, making the direction and volume of movement the central visual element.
Who is considered the key innovator behind flow maps?
Charles Joseph Minard is widely credited as the pioneering figure, producing landmark flow-map illustrations during the 1840s through the 1870s. His work set the visual and conceptual template that later cartographers built upon.
What kinds of movement can a flow map depict?
Flow maps can represent anything that travels across space: people migrating, highway traffic, trade goods, water currents, ideas, or telecommunications data. The wide range of possible subjects has driven cartographers to develop many different design strategies for encoding volume, direction, and origin-destination pairs.
How does a flow map differ from a standard thematic map?
While a typical thematic map shades regions or places points to show a static attribute, a flow map specifically encodes the act of movement between locations using linear symbols. Its primary purpose is to make the path and magnitude of transfer visible rather than to classify a fixed area.
Do cartographers all agree on what counts as a flow map?
Not quite. Some practitioners use the term broadly to cover any thematic map of a linear network, while others insist it must explicitly depict movement from one point to another. This definitional split is one reason the category can look quite different across textbooks and atlases.
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