In geography, arrows drawn on a map to show movement are called flow lines. They connect an origin with a destination and indicate the direction in which people, goods, money, traffic, migration, wind, or other phenomena move.
Flow lines are often drawn with different widths. A thicker line can represent a larger volume of movement, while a thinner line represents a smaller flow. For example, a migration map may use broad arrows for major population movements and narrow arrows for smaller ones. The map’s legend explains exactly how line width, color, or other symbols should be interpreted.
Flow lines are related to flow maps, which are the complete thematic maps that display these movements. They are sometimes confused with desire lines: desire lines show a general connection or direction between places, whereas flow lines are typically used to represent actual movement and may show its magnitude. Historical examples include maps of trade, military campaigns, railway traffic, and migration.