Flow maps are characterized by representing direction and amount of movement between an origin and a destination – and Charles Joseph Minard is widely regarded as the first cartographer who mastered the art of the flow map. He is best known for his flow map of Napolean’s 1812 invasion of Russia titled “Carte figurative des pertes successives en hommes de l’armée française dans la campagne de Russie 1812-1813,” published in 1869, but many of his lesser-known earlier works are fascinating in their own right.
While modern digital mapping techniques have changed the way flow maps are created, Minard’s work stands out as encompassing all the techniques of graphical illustration that geographers still seek to achieve in flow maps made today. His aim was to allow a map reader to quickly understand the magnitude and direction of statistical geographic data that would otherwise need to be communicated through more complex graphs or charts.
Many of Minard’s early maps document the movement of goods and people during a period of global colonization and slavery. In the above flow map from 1862, Minard mapped global flows of human migration for the year 1858. The number of emigrants are represented by the colored lines at the rate of one millimeter for each 1,500 emigrants.
These numbers are also written across the lines with a unit of one thousand emigrants. Looking at the lines in detail, you can see the number of emigrants rise and fall as flow lines merge and depart from each other. Seen in the detailed image on the left, the map documents flows of Africans departing Central Africa for Reunion and Mauritius, at the time French and British colonies. Also visible on the full maps are flows of Africans into the Caribbean alongside lines from China and South Asia. In 1858, slavery was not yet abolished globally, which means this movement of people includes forced migration through slavery or indentured servitude. The map also shows the heavy movement from northern Europe into the United States, as well as British emigrants who moved to Canada, the United States, and Australia (which would include the movement of British prisoners to Australia).
Another of Minard’s creations shows the global cotton trade over time: comparing the flow of cotton in 1858 and 1861.
In both the 1858 and 1861 illustrations, the flow of cotton exports out of the United States into Europe and England dominate with map. In 1858, slavery in the southern United States was actively producing huge amounts of cotton at such volumes that many southern states believed the cotton industry could sustain their secession from the United States. 1861 marks the year southern states seceded and American Civil War broke out, at which point the United States blocked Confederate ports. Eventually the Confederacy itself stopped selling cotton to Europe and the United Kingdom in an attempt to pressure them into supporting their side during the war. The United Kingdom more than doubled their imports of cotton from India from 70,000 tons to 180,000 tons to compensate.
Minard also mapped the flow of cotton at the end of the American Civil War, showing 1858 numbers against 1864 and 1865 with each millimeter of line representing five thousand tons of cotton. The resulting map shows the ebb and flow of American cotton dominance, from the height of “King Cotton” in 1858 during a period of legal slavery, the shift to a reliance on Indian cotton by 1864, and a rebalancing in 1865 as the Civil War ended. After the war, southern plantation owners were allowed to keep their land, allowing for the creation of a system of share-cropping that would come to dominate the cotton industry. Also notable is the expansion of cotton exports from Northern Africa and the Middle East to the United Kingdom during this period.
As fights over human freedom shifted the global economy and movement of goods and people during the 1860s, Minard’s flow maps served to make complex global processes legible to the casual map reader, a feat many still strive to achieve today.