This is a distinctive early government thematic flow map displaying the volume of maritime trade along the ports from San Francisco to Washington. The map indicates that nearly 1.7 million tons of cargo headed north of San Francisco, with about half going through the Strait of Juan de Fuca, and the other half going to smaller ports in between including the Columbia River and Humboldt River. This chart was used in the planning for harbors of refuge along the Pacific Coast and is an excellent example of the type of economic geography flow map innovated by Charles Minard beginning in the 1840s.

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Condition: A

Issued folding with light toning along the sheet edges.