What symbol is used to show migration routes

Flow maps are a kind of thematic map used in cartography to demonstrate the movement of objects between unalike areas. These types of maps can show things like the movement of goods across space, the number of animal species in a specific migration pattern, as well as traffic volume and stream flow. They can also display both qualitative and quantitative data. Flow maps usually represent the movement of goods, weather phenomena, people and other living things with line symbols of different widths. Thus, the use of flow lines on a flow map is comparable to the use of graduated symbols on other types of thematic maps. These lines are often used to show migration, trade and other intercourse between areas. 

answer:    

a.

explanation:

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